Communication system

ABSTRACT

A communication system is provided that, if a large number of small cells are installed, is capable of configuring an operation suitable for small cells through simple operation and administration. If a small cell installed in Step ST1401 judges in Step ST1403 that a coverage macro cell, which includes the small cell in the coverage of the coverage macro cell, is present as a result of neighbor cell search in Step ST1402, notifies the coverage macro cell and another neighbor cell of its own capability in Steps ST1404 and 1405. The coverage macro cell selects a configuration parameter suitable for the capability of the small cell in Step ST1406 and notifies the small cell in Step ST1407. The small cell recognizes an operation mode configured by the coverage macro cell from the configuration parameter notified from the coverage macro cell, and then, starts operating in the operation mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present continuation application is based upon and claims thebenefit of priority from U.S. application Ser. No. 14/767,501, filed onAug. 12, 2015, which is based upon and claims priority from priorInternational Application No. PCT/JP2014/053291, filed on Feb. 13, 2014,which claims priority from Japanese Patent Application No. 2013-027801filed on Feb. 15, 2013; the entire contents of which are herebyincorporated by reference into this application.

TECHNICAL FIELD

The present invention relates to a communication system including anetwork device connected to a core network and a communication terminaldevice that performs radio communication via the network device.

BACKGROUND ART

Commercial service of a wideband code division multiple access (W-CDMA)system among so-called third-generation communication systems has beenoffered in Japan since 2001. In addition, high speed downlink packetaccess (HSDPA) service for achieving higher-speed data transmissionusing a downlink has been offered by adding a channel for packettransmission (high speed-downlink shared channel (HS-DSCH)) to thedownlink (dedicated data channel, dedicated control channel). Further,in order to increase the speed of data transmission in an uplinkdirection, service of a high speed uplink packet access (HSUPA) systemhas been offered. W-CDMA is a communication system defined by the 3rdgeneration partnership project (3GPP) that is the standard organizationregarding the mobile communication system, where the specifications ofRelease 10 version are produced.

Further, 3GPP is studying new communication systems referred to as longterm evolution (LTE) regarding radio sections and system architectureevolution (SAE) regarding the overall system configuration including acore network and a radio access network (hereinafter, collectivelyreferred to as a network as well) as communication systems independentof W-CDMA. This communication system is also referred to as 3.9generation (3.9 G) system.

In the LTE, an access scheme, a radio channel configuration, and aprotocol are totally different from those of the W-CDMA (HSDPA/HSUPA).For example, as to the access scheme, code division multiple access isused in the W-CDMA, whereas in the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. In addition, the bandwidth is 5 MHz in the W-CDMA, while inthe LTE, the bandwidth can be selected from 1.4 MHz, 3 MHz, 5 MHz, 10MHz, 15 MHz, and 20 MHz per base station. Further, differently from theW-CDMA, circuit switching is not provided but a packet communicationsystem is only provided in the LTE.

In the LTE, a communication system is configured with a new core networkdifferent from the general packet radio service (GPRS) being the corenetwork of the W-CDMA, and thus, the radio access network of the LTE isdefined as a radio access network independent of the W-CDMA network.

Therefore, for differentiation from the W-CDMA communication system, acore network and a radio access network are referred to as an evolvedpacket core (EPC) and an evolved universal terrestrial radio accessnetwork (E-UTRAN), respectively, in the LTE communication system. Alsoin the radio access network, the base station that communicates with amobile terminal (user equipment (UE)) being a communication terminaldevice is referred to as an E-UTRAN NodeB (eNB). The EPC functions as aradio network controller that exchanges control data and user data witha plurality of base stations. The EPC is also referred to as an accessgateway (aGW). The system formed of the EPC and E-UTRAN is referred toas an evolved packet system (EPS).

Unicast service and evolved multimedia broadcast multicast service(E-MBMS service) are provided in the LTE communication system. TheE-MBMS service is broadcast multimedia service. The E-MBMS service ismerely referred to as IN/IBMS in some cases. Bulk broadcast contentssuch as news, weather forecast, and mobile broadcast are transmitted toa plurality of user equipments in the E-MBMS service. This is alsoreferred to as point to multipoint service.

Non-Patent Document 1 (Chapter 4) describes the current decisions by3GPP regarding an overall architecture in the LTE system. The overallarchitecture will be described with reference to FIG. 1. FIG. 1 is adiagram illustrating the configuration of the LTE communication system.With reference to FIG. 1, the E-UTRAN is composed of one or a pluralityof base stations 102, provided that a control protocol for a userequipment 101 such as a radio resource control (RRC), and user planessuch as a packet data convergence protocol (PDCP), radio link control(RLC), medium access control (MAC), or physical layer (PHY) are ended inthe base station 102.

The base stations 102 perform scheduling and transmission of a pagingsignal (also referred to as paging messages) notified from a mobilitymanagement entity (MME) 103. The base stations 102 are connected to eachother by means of an X2 interface. In addition, the base stations 102are connected to an evolved packet core (EPC) by means of an S1interface. More specifically, the base station 102 is connected to themobility management entity (MME) 103 by means of an S1_MME interface andconnected to a serving gateway (S-GW) 104 by means of an S1_U interface.

The MME 103 distributes the paging signal to a plurality of or a singlebase station 102. In addition, the MME 103 performs mobility control ofan idle state. When the user equipment is in the idle state and anactive state, the MME 103 manages a list of tracking areas.

The S-GW 104 transmits/receives user data to/from one or a plurality ofbase stations 102. The S-GW 104 serves as a local mobility anchor pointin handover between base stations. Moreover, a PDN gateway (P-GW) isprovided in the EPC. The P-GW performs per-user packet filtering andUE-ID address allocation.

The control protocol RRC between the user equipment 101 and the basestation 102 performs broadcast, paging, RRC connection management, andthe like. The states of the base station and the user equipment in RRCare classified into RRC_IDLE and RRC_CONNECTED. In RRC_IDLE, public landmobile network (PLMN) selection, system information (SI) broadcast,paging, cell reselection, mobility, and the like are performed. InRRC_CONNECTED, the user equipment has RRC connection and is capable oftransmitting/receiving data to/from a network. In RRC_CONNECTED, forexample, handover (HO) and measurement of a neighbor cell are performed.

The current decisions by 3GPP regarding the frame configuration in theLTE system described in Non-Patent Document 1 (Chapter 5) will bedescribed with reference to FIG. 2. FIG. 2 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 2, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per each radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).

Multiplexing of channels for multimedia broadcast multicast servicesingle frequency network (MBSFN) and for non-MBSFN is performed on aper-subframe basis. MBSFN transmission is the simulcast transmissiontechnique realized by simultaneous transmission of the same waveformsfrom a plurality of cells. The MBSFN transmission from a plurality ofcells in the MBSFN area is seen as a single transmission by a userequipment. The MBSFN is a network that supports such MBSFN transmission.Hereinafter, a subframe for MBSFN transmission is referred to as anMBSFN subframe.

Non-Patent Document 2 describes a signaling example when MBSFN subframesare allocated. FIG. 3 is a diagram illustrating the configuration of theMBSFN frame. As shown in FIG. 3, the radio frames including the MBSFNsubframes are allocated per radio frame allocation period. The MBSFNsubframe is a subframe allocated for the MBSFN in a radio frame definedby the allocation period and the allocation offset (radio frameallocation offset), which serves to transmit multimedia data. The radioframe satisfying Equation (1) below is a radio frame including the MBSFNsubframes.SFN mod radioFrameAllocationPeriod=radioFrameAllocationOffset  (1)

The MBSFN subframe is allocated with six bits. With reference to FIG. 3,the leftmost bit defines the MBSFN allocation for the second subframe(#1). The second bit, third bit, fourth bit, fifth bit, and sixth-bitfrom the left define the MBSFN allocation for the third subframe (#2),fourth subframe (#3), seventh subframe (#6), eighth subframe (#7), andninth subframe (#8), respectively. The case where the bit indicates“one” represents that a corresponding subframe is allocated for theMBSFN.

Non-Patent Document 1 (Chapter 5) describes the current decisions by3GPP regarding the channel configuration in the LTE system. It isassumed that the same channel configuration is used in a closedsubscriber group (CSG) cell as that of a non-CSG cell. Physical channelsare described with reference to FIG. 4. FIG. 4 is a diagram illustratingphysical channels used in the LTE communication system.

With reference to FIG. 4, a physical broadcast channel (PBCH) 401 is achannel for downlink transmission from the base station 102 to the userequipment 101. A BCH transport block is mapped to four subframes withina 40 ms interval. There is no explicit signaling indicating 40 mstiming.

A physical control format indicator channel (PCFICH) 402 is a channelfor downlink transmission from the base station 102 to the userequipment 101. The PCFICH notifies the number of OFDM symbols used forPDCCHs from the base station 102 to the user equipment 101. The PCFICHis transmitted in each subframe.

A physical downlink control channel (PDCCH) 403 is a channel fordownlink transmission from the base station 102 to the user equipment101. The PDCCH notifies the resource allocation information for downlinkshared channel (DL-SCH) being one of the transport channels shown inFIG. 5 described below, resource allocation information for a pagingchannel (PCH) being one of the transport channels shown in FIG. 5, andhybrid automatic repeat request (HARQ) information related to DL-SCH.The PDCCH carries an uplink scheduling grant. The PDCCH carriesacknowledgement (Ack) negative acknowledgement (Hack) that is a responsesignal to uplink transmission. The PDCCH is referred to as an L1/L2control signal as well.

A physical downlink shared channel (PDSCH) 404 is a channel for downlinktransmission from the base station 102 to the user equipment 101. Adownlink shared channel (DL-SCH) that is a transport channel and a PCHthat is a transport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) 405 is a channel for downlinktransmission from the base station 102 to the user equipment 101. Amulticast channel (MCH) that is a transport channel is mapped to thePMCH.

A physical uplink control channel (PUCCH) 406 is a channel for uplinktransmission from the user equipment 101 to the base station 102. ThePUCCH carries Ack/Nack that is a response signal to downlinktransmission. The PUCCH carries a channel quality indicator (CQI)report. The CQI is quality information indicating the quality ofreceived data or channel quality. In addition, the PUCCH carries ascheduling request (SR).

A physical uplink shared channel (PUSCH) 407 is a channel for uplinktransmission from the user equipment 101 to the base station 102. Anuplink shared channel (UL-SCH) that is one of the transport channelsshown in FIG. 5 is mapped to the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) 408 is a channel fordownlink transmission from the base station 102 to the user equipment101. The PHICH carries Ack/Nack that is a response signal to uplinktransmission. A physical random access channel (PRACH) 409 is a channelfor uplink transmission from the user equipment 101 to the base station102. The PRACH carries a random access preamble.

A downlink reference signal (RS) is a known symbol in the LTEcommunication system. The following five types of downlink referencesignals are defined: cell-specific reference signals (CRS), MBSFNreference signals, data demodulation reference signal (DM-RS) beingUE-specific reference signals, positioning reference signals (PRS), andchannel-state information reference signals (CSI-RS). The physical layermeasurement objects of a user equipment include reference signalreceived power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described with reference to FIG. 5. FIG. 5 is a diagramillustrating transport channels used in the LTE communication system.Part (A) of FIG. 5 shows mapping between downlink transport channels anddownlink physical channels. Part (B) of FIG. 5 shows mapping betweenuplink transport channels and uplink physical channels.

A broadcast channel (BCH) among the downlink transport channels shown inPart (A) of FIG. 5 is broadcast to the entire coverage of a base station(cell). The BCH is mapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH can be broadcasted to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a user equipment for enabling the userequipment to save power. The DL-SCH is mapped to the physical downlinkshared channel (PDSCH).

The paging channel (PCH) supports DRX of the user equipment for enablingthe user equipment to save power. The PCH is required to be broadcast tothe entire coverage of the base station (cell). The PCH is mapped tophysical resources such as the physical downlink shared channel (PDSCH)that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of MBMSservices (MTCH and MCCH) in multi-cell transmission. The MCH supportssemi-static resource allocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels shownin Part (B) of FIG. 5. The UL-SCH supports dynamic or semi-staticresource allocation. The UL-SCH is mapped to the physical uplink sharedchannel (PUSCH).

A random access channel (RACH) shown in Part (B) of FIG. 5 is limited tocontrol information. The RACH involves a collision risk. The RACH ismapped to the physical random access channel (PRACH).

The HARQ will be described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest (ARQ) and error correction (forward error correction). The HARQis advantageous in that error correction functions effectively byretransmission even for a channel whose communication quality changes.In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. If thereceiver fails to successfully decode the received data, in other words,if a cyclic redundancy check (CRC) error occurs (CRC=NG), the receivertransmits “Nark” to the transmitter. The transmitter that has received“Nark” retransmits the data. If the receiver successfully decodes thereceived data, in other words, if a CRC error does not occur (CRC=OK),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data.

Examples of the HARQ system include chase combining. In chase combining,the same data is transmitted in the first transmission andretransmission, which is the system for improving gains by combining thedata of the first transmission and the data of the retransmission inretransmission. Chase combining is based on the idea that correct datais partially included even if the data of the first transmissioncontains an error, and highly accurate data transmission is enabled bycombining the correct portions of the first transmission data and theretransmission data. Another example of the HARQ system is incrementalredundancy (IR). The IR is aimed to increase redundancy, where a paritybit is transmitted in retransmission to increase the redundancy bycombining the first transmission and retransmission, to thereby improvethe quality by an error correction function.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described with reference to FIG. 6. FIG. 6 is a diagram illustratinglogical channels used in an LTE communication system. Part (A) of FIG. 6shows mapping between downlink logical channels and downlink transportchannels. Part (B) of FIG. 6 shows mapping between uplink logicalchannels and uplink transport channels.

A broadcast control channel (BCCH) is a downlink channel for broadcastsystem control information. The BCCH that is a logical channel is mappedto the broadcast channel (BCH) or downlink shared channel (DL-SCH) thatis a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging information and system information change notifications. The PCCHis used when the network does not know the cell location of a userequipment. The PCCH that is a logical channel is mapped to the pagingchannel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between user equipments and a base station. The CCCH is usedin the case where the user equipments have no RRC connection with thenetwork. In a downlink direction, the CCCH is mapped to the downlinkshared channel (DL-SCH) that is a transport channel. In an uplinkdirection, the CCCH is mapped to the uplink shared channel (UL-SCH) thatis a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to auser equipment. The MCCH is used only by a user equipment duringreception of the MBMS. The MCCH is mapped to the multicast channel (MCH)that is a transport channel.

A dedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a user equipment and a network on apoint-to-point basis. The DCCH is used if the user equipment has an RRCconnection. The DCCH is mapped to the uplink shared channel (UL-SCH) inuplink and mapped to the downlink shared channel (DL-SCH) in downlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a user equipment. The MTCH is achannel used only by a user equipment during reception of the MBMS. TheMTCH is mapped to the multicast channel (MCH).

CGI represents a cell global identifier. ECGI represents an E-UTRAN cellglobal identifier. A closed subscriber group (CSG) cell is introduced inthe LTE, and the long term evolution advanced (LTE-A) and universalmobile telecommunication system (UNITS) described below. The CSG cellwill be described below (see Chapter 3.1 of Non-Patent Document 3).

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed to use are specified by an operator (also referred to asa “cell for specific subscribers”). The specified subscribers areallowed to access one or more cells of a public land mobile network(PLMN). One or more cells in which the specified subscribers are allowedaccess are referred to as “CSG cell(s).” Note that access is limited inthe PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID; CSG-ID) and broadcasts “TRUE” in a CSG indication. Theauthorized members of the subscriber group who have registered inadvance access the CSG cells using the CSG-ID that is the accesspermission information.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in the LTE communication system. The CSG-IDs are used by userequipments (UEs) for making access from CSG-related members easier.

The locations of user equipments are tracked on the basis of an areacomposed of one or more cells. The locations are tracked for enablingtracking the locations of user equipments and calling user equipments,in other words, incoming calling to user equipments even in an idlestate. An area for tracking locations of user equipments is referred toas a tracking area.

The CSG whitelist is a list that may be stored in a universal subscriberidentity module (USIM) in which all CSG IDs of the CSG cells to whichthe subscribers belong are recorded. The CSG whitelist may be merelyreferred to as a whitelist or an allowed CSG list as well. As to theaccess of user equipments through a CSG cell, the MME performs accesscontrol (see Chapter 4.3.1.2 of Non-Patent Document 4). Specificexamples of the access of user equipments include attach, combinedattach, detach, service request, and a tracking area update procedure(see Chapter 4.3.1.2 of Non-Patent Document 4).

Described below is the service types of a user equipment in an idlestate (see Chapter 4.3 of Non-Patent Document 3). The service types ofuser equipments in an idle state include a limited service, normalservice, and operator service. The limited service includes emergencycalls, earthquake and tsunami warning system (ETWS), and commercialmobile alert system (CMAS) on an acceptable cell described below. Thenormal service is a public service on a suitable cell described below.The operator service includes a service for operators only on a reservedcell described below.

Described below is a “suitable cell”. The “suitable cell” is a cell onwhich a UE may camp (Camp ON) to obtain normal service. Such a cellshall fulfill the following conditions (1) and (2).

(1) The cell is part of the selected PLMN or the registered PLMN, orpart of the PLMN of an “equivalent PLMN list.”

(2) According to the latest information provided by a non-access stratum(NAS), the cell shall further fulfill the following conditions (a) to(d):

(a) the cell is not a barred cell;

(b) the cell is part of a tracking area, not part of the list of“forbidden LAs for roaming,” where the cell needs to fulfill (1) above;

(c) the cell shall fulfill the cell selection criteria; and

(d) for a cell specified as CSG cell by system information (SI), theCSG-ID is part of a “CSG whitelist” of the UE, that is, is contained inthe CSG whitelist of the UE.

Described below is an “acceptable cell.” The “acceptable cell” is thecell on which a UE may camp to obtain limited service. Such a cell shallfulfill all the following requirements (1) and (2).

(1) The cell is not a prohibited cell (also referred to as a “barredcell”).

(2) The cell fulfills the cell selection criteria.

“Barred cell” is indicated in the system information. “Reserved cell” isindicated in the system information.

“Camping on a cell” represents the state where a UE has completed thecell selection or cell reselection process and the UE has selected acell for monitoring the system information and paging information. Thecell on which the UE camps may be referred to as a “serving cell.”

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 5 discloses three different modes ofthe access to the HeNB and HNB. Specifically, an open access mode, aclosed access mode, and a hybrid access mode are disclosed.

The respective modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a CSG cell where only CSG members are allowedaccess. In the hybrid access mode, the HeNB and HNB are operated as CSGcells where non-CSG members are allowed access at the same time. Inother words, a cell in the hybrid access mode (also referred to as ahybrid cell) is the cell that supports both the open access mode and theclosed access mode.

In 3GPP, among all physical cell identities (PCIs), there is a range ofPCIs reserved by the network for use by CSG cells (see Chapter 10.5.1.1of Non-Patent Document 1). Division of the PCI range is also referred toas PCI split. The information about PCI split (also referred to as PCIsplit information) is broadcast in the system information from a basestation to user equipments being served thereby. To be served by a basestation means to take the base station as a serving cell.

Non-Patent Document 6 discloses the basic operation of a user equipmentusing PCI split. The user equipment that does not have the PCI splitinformation needs to perform cell search using all PCIs, for example,using all 504 codes. On the other hand, the user equipment that has thePCI split information is capable of performing cell search using the PCIsplit information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 7 and 8).

As to the LTE-A system, it is studied that a relay and a relay node (RN)are supported for achieving a high data rate, high cell-edge throughput,new coverage area, and the like. The relay node being a relay device iswirelessly connected to the radio-access network via a cell referred toas a donor cell (hereinafter, also referred to as a “Donor eNB; DeNB”).The network (NW)-to-relay node link shares the same frequency band withthe network-to-UE link within the range of the donor cell. In this case,the UE supporting Release 8 of 3GPP is also connectable to the donorcell. The link between the donor cell and the relay node is referred toas a backhaul link, and the link between the relay node and the UE isreferred to as an access link.

As the method of multiplexing a backhaul link in frequency divisionduplex (FDD), the transmission from a DeNB to an RN is performed at adownlink (DL) frequency band, and the transmission from an RN to a DeNBis performed at an uplink (UL) frequency band. As the method of dividingresources in a relay, a link from a DeNB to an RN and a link from an RNto a UE are time-division multiplexed at one frequency band, and a linkfrom an RN to a DeNB and a link from a UE to an RN are alsotime-division multiplexed at one frequency band. In a relay,accordingly, the transmission of the relay is prevented from interferingthe reception of its own relay.

Not only a normal eNB (macro cell) but also so-called local nodes suchas pico eNB (pico cell), HeNB (HNB, CSG cell), node for hotzone cells,relay node, remote radio head (RRH), and repeater are studied in 3GPP.The network composed of various types of cells as described above isalso referred to as a heterogeneous network (HetNet) in some cases.

The frequency bands (hereinafter, also referred to as “operating bands”)usable for communication have been predetermined in the LTE. Non-PatentDocument 9 describes the frequency bands.

Carrier aggregation (CA) is studied in the LTE-A system, in which two ormore component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz.

A UE supporting Release 8 or 9 of 3GPP, which supports LTE, is capableof transmission and reception on only one CC corresponding to oneserving cell. Meanwhile, it is conceivable that a UE supporting Release10 of 3GPP may have the capability of transmission and reception, onlyreception, or only transmission on a plurality of CCs corresponding to aplurality of serving cells at the same time.

Each CC employs the configuration of Release 8 or 9 of 3GPP, and the CAsupports contiguous CCs, non-contiguous CCs, and CCs in differentfrequency bandwidths. The UE cannot configure uplink CCs (UL CCs) equalto or more than the number of downlink CCs (DL CCs). The CCs configuredby the same eNB do not need to provide the same coverage. The CC iscompatible with Release 8 or 9 of 3GPP.

In CA, an independent HARQ entity is provided per serving cell in uplinkas well as downlink. A transport block is generated per TTI for eachserving cell. Each transport block and HARQ retransmission are mapped toa single serving cell.

In the case where CA is configured, a UE has a single RRC connectionwith a NW. In RRC connection, one serving cell provides NAS mobilityinformation and security input. This cell is referred to as a primarycell (PCell). In downlink, a carrier corresponding to PCell is adownlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a serving cell group witha PCell, in accordance with the UE capability. In downlink, a carriercorresponding to SCell is a downlink secondary component carrier (DLSCC). In uplink, a carrier corresponding to SCell is an uplink secondarycomponent carrier (UL SCC).

A serving cell group of one PCell and one or more SCell is configuredfor one UE.

The above-mentioned LTE Advanced (LTE-A) is studied as a furtheradvanced communication system regarding radio sections in 3GPP (seeNon-Patent Documents 7 and 8). The LTE-A is based on the LTEcommunication system regarding radio sections and is configured byaddition of several new techniques thereto. The new techniques includethe technique of supporting wider bands (wider bandwidth extension) andthe coordinated multiple point transmission and reception (CoMP)technique. The CoMP studied for LTE-A in 3GPP is described in Non-PatentDocument 10.

CoMP is the technique of expanding the coverage of high data rates,improving a cell-edge throughput, and increasing a communication systemthroughput by transmission or reception coordinated among multiplegeographically separated points. The CoMPs are grouped into downlinkCoMP (DL CoMP) and uplink CoMP (UL CoMP).

In DL CoMP, the PDSCH to one user equipment (UE) is transmitted incooperation among multiple points. The PDSCH to one UE may betransmitted from one point among multiple points or may be transmittedfrom points among multiple points. In DL CoMP, a serving cell refers toa single cell that transmits resource allocation over the PDCCH.

Joint processing (JP) and coordinated scheduling (CS)/coordinatedbeamforming (CB) (hereinafter, also referred to as “CS/CB”) are studiedas the DL CoMP method.

For JP, data is available at each point in a CoMP cooperating set. JPsare grouped into Joint transmission (JT) and dynamic point selection(DPS). DPSs include dynamic cell selection (DCS). In JT, the PDSCH istransmitted from multiple points, specifically, part of or entire CoMPcooperating set, at a time. In DPS, the PDSCH is transmitted from onepoint in the CoMP cooperating set at a time.

In CS/CB, data is only available in transmission from a serving cell. InCS/CB, user scheduling or beamforming decisions are made withcoordination among cells corresponding to the CoMP cooperating set.

Base stations (NB, eNB, HNB, HeNB), remote radio unit (RRU), remoteradio equipment (RRE), remote radio head (RRH), relay node (RN), and thelike are studied as the units and cells that perform transmission andreception at multiple points. The unit and cell that perform coordinatedmultiple point transmission are also referred to as a multi-point unitand a multi-point cell, respectively.

3GPP is pursuing specifications standard of Release 12, where the use ofsmall eNBs (cells) is studied to satisfy a tremendous volume of trafficin the future. Examples of the study include the technique of increasingspectral efficiency through installation of a large number of small eNBs(cells) to increase communication capacity.

PRIOR ART DOCUMENTS Non-Patent Documents

Non-Patent Document 1: 3GPP TS 36.300 V11.4.0

Non-Patent Document 2: 3GPP TS 36.331 V11.0.0

Non-Patent Document 3: 3GPP TS 36.304 V11.1.0, Chapter 3.1, Chapter 4.3,Chapter 5.2.4

Non-Patent Document 4: 3GPP TR 23.830 V9.0.0

Non-Patent Document 5: 3GPP S1-083461

Non-Patent Document 6: 3GPP R2-082899

Non-Patent Document 7: 3GPP TR 36.814 V9.0.0

Non-Patent Document 8: 3GPP TR 36.912 V10.0.0

Non-Patent Document 9: 3GPP TS 36.101 V11.0.0

Non-Patent Document 10: 3GPP TR 36.819 V11.1.0

SUMMARY OF INVENTION Problem to be Solved by the Invention

As the places in which small cells are installed, the following arestudied: a place within the coverage (hereinafter, also referred to asthe “coverage of a macro cell”) of a macro eNB (hereinafter, alsoreferred to as a “macro cell”) and a place outside the coverage of amacro cell. Installation of a large number of small cells is alsostudied.

Conventional operation and administration of each small cell by anoperator, in which the cell's installation place or the like is takeninto account, results in complicated work for the operator.

The present invention has an object to provide a communication systemcapable of configuring, if a large number of small cells are installed,an operation suitable for the small cells through simple operation andadministration.

Means to Solve the Problem

A communication system according to the present invention includes anetwork device that is connected to a core network and a communicationterminal device that performs radio communication via the networkdevice. The network device includes a plurality of base station deviceseach having a range predetermined as a coverage in which communicationwith the communication terminal device is enabled and configuring a cellthat performs radio communication with the communication terminal devicein the coverage, and a higher-level device located on the core networkside relative to the base station device. The plurality of base stationdevices include a large-scale base station device configuring a macrocell being a cell having a relatively-wide-range coverage as thecoverage, and a small-scale base station device configuring a small cellbeing a cell having a relatively-narrow-range coverage as the coverage.The small cell notifies the network device including at least one ofanother cell and the higher-level device of capability informationindicating a capability of the small cell. The network device notifiedof the capability information performs, on the small cell, aconfiguration suitable for the capability of the small cell on the basisof the notified capability information.

Effects of the Invention

According to the communication system of the present invention, thenetwork device performs a configuration suitable for the capability ofthe small cell, thereby allowing, when a small cell is installed, thesmall cell to start operating without an operator. This achieves easyoperation and administration by the operator when the small cell isinstalled. Therefore, if a large number of small cells are installed, acommunication system capable of configuring an operation suitable forthe small cells is achieved through simple operation and administration.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an LTEcommunication system.

FIG. 2 is a diagram illustrating the configuration of a radio frame usedin the LTE communication system.

FIG. 3 is a diagram illustrating the configuration of an MBSFN frame.

FIG. 4 is a diagram illustrating physical channels used in the LTEcommunication system.

FIG. 5 is a diagram illustrating transport channels used in the LTEcommunication system.

FIG. 6 is a diagram illustrating logical channels used in the LTEcommunication system.

FIG. 7 is a block diagram showing the overall configuration of an LTEcommunication system currently under discussion of 3GPP.

FIG. 8 is a block diagram showing the configuration of a user equipment71 of FIG. 7 being a user equipment according to the present invention.

FIG. 9 is a block diagram showing the configuration of a base station 72of FIG. 7 being a base station according to the present invention.

FIG. 10 is a block diagram showing the configuration of an MME unit 73of FIG. 7 being an MME according to the present invention.

FIG. 11 is a block diagram showing the configuration of a HeNBGW 74 ofFIG. 7 being a HeNBGW according to the present invention.

FIG. 12 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

FIG. 13 shows the concept of the configuration of conventional cells.

FIG. 14 shows the concept of the configuration of downsized cells.

FIG. 15 shows the concept of the configuration of cells in which macroeNBs (macro cells) and small eNBs (small cells) coexist.

FIG. 16 shows an example sequence of a communication system in a firstembodiment.

FIG. 17 shows the example sequence of the communication system in thefirst embodiment.

FIG. 18 shows an example sequence of a communication system in a secondembodiment.

FIG. 19 shows the example sequence of the communication system in thesecond embodiment.

FIG. 20 shows another example sequence of the communication system inthe second embodiment.

FIG. 21 shows the other example sequence of the communication system inthe second embodiment.

FIG. 22 shows an example sequence of a communication system in a firstmodification of the second embodiment.

FIG. 23 shows the example sequence of the communication system in thefirst modification of the second embodiment.

FIG. 24 shows another example sequence of the communication system inthe first modification of the second embodiment.

FIG. 25 shows the other example sequence of the communication system inthe first modification of the second embodiment.

FIG. 26 is a diagram for explaining the concept of a solution of a thirdmodification of the second embodiment.

DESCRIPTION OF EMBODIMENTS

First Embodiment

FIG. 7 is a block diagram showing an overall configuration of an LTEcommunication system, which is currently under discussion of 3GPP. 3GPPhas studied an overall configuration of a system including closedsubscriber group (CSG) cells (Home-eNodeBs (Home-eNB; HeNB) of E-UTRAN,Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB (eNB) of E-UTRAN,NodeB (NB) of UTRAN, and BSS of GERAN) and, as to E-UTRAN, has proposedthe configuration as shown in FIG. 7 (see Chapter 4.6.1 of Non-PatentDocument 1).

FIG. 7 will be described. A mobile terminal device (hereinafter,referred to as a “user equipment (UE)”) 71 being a communicationterminal device is capable of radio communication with a base stationdevice (hereinafter, referred to as a “base station”) 72 and transmitsand receives signals through radio communication. The base stations 72are classified into eNBs 72-1 and Home-eNBs 72-2.

The eNB 72-1 is connected to an MME/S-GW unit (hereinafter, alsoreferred to as an “MME unit”) 73 including an MME, an S-GW, or an MMEand an S-GW by means of an S1 interface, and control information iscommunicated between the eNB 72-1 and the MME unit 73. A plurality ofMME units 73 may be connected to one eNB 72-1. The MME unit 73 isincluded in an EPC being a core network. The eNBs 72-1 are connected toeach other by means of an X2 interface, and control information iscommunicated between the eNBs 72-1.

The Home-eNB 72-2 is connected to the MME unit 73 by means of an S1interface, and control information is communicated between the Home-eNB72-2 and the MME unit 73. A plurality of Home-eNBs 72-2 are connected toone MME unit 73. Or, the Horne-eNBs 72-2 are connected to the MME units73 through a Home-eNB gateway (HeNBGW) 74. The Home-eNB 72-2 isconnected to the HeNBGW 74 by means of an S1 interface, and the HeNBGW74 is connected to the MME unit 73 through an S1 interface.

One or a plurality of Home-eNBs 72-2 are connected to one HeNBGW 74, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 74 is connected to one or a plurality of MME units 73, andinformation is communicated therebetween through an S1 interface.

The MME units 73 and HeNBGW 74 are devices of higher nodes and controlthe connections between the user equipment (UE) 71 and the eNB 72-1 andHome-eNB 72-2 being base stations. The MME units 73 and HeNBGW 74 areincluded in the EPC being a core network.

Further, 3GPP has studied the configuration below. The X2 interfacebetween the Home-eNBs 72-2 is supported. In other words, the Home-eNBs72-2 are connected to each other by means of an X2 interface, andcontrol information is communicated between the Home-eNBs 72-2. TheHeNBGW 74 appears to the MME unit 73 as the Home-eNB 72-2. The HeNBGW 74appears to the Home-eNB 72-2 as the MME unit 73.

The interfaces between the Home-eNBs 72-2 and the MME units 73 are thesame, which are the S1 interfaces, in both cases where the Home-eNB 72-2is connected to the MME unit 73 through the HeNBGW 74 and it is directlyconnected to the MME unit 73. The HeNBGW 74 does not support themobility to the Home-eNB 72-2 or the mobility from the Home-eNB 72-2that spans a plurality of MME units 73. The Home-eNB 72-2 configures asingle cell.

The base station device configures a single cell, such as the Home-eNB72-2, which is not limited thereto. One base station device may supporta plurality of cells. The cell has a range predetermined as a coveragein which the cell can communicate with a communication terminal deviceand performs radio communication with the communication terminal devicewithin the coverage. In the case where one base station deviceconfigures a plurality of cells, every cell is configured to communicatewith a mobile terminal.

FIG. 8 is a block diagram showing the configuration of the userequipment 71 of FIG. 7 being a user equipment according to the presentinvention. The transmission process of the user equipment 71 shown inFIG. 8 will be described. First, a transmission data buffer unit 803stores the control data from a protocol processing unit 801 and the userdata from an application unit 802. The data stored in the transmissiondata buffer unit 803 is passed to an encoding unit 804 and is subjectedto an encoding process such as error correction. There may exist thedata output from the transmission data buffer unit 803 directly to amodulating unit 805 without the encoding process. The data encoded bythe encoding unit 804 is modulated by the modulating unit 805. Themodulated data is converted into a baseband signal, and the basebandsignal is output to a frequency converting unit 806 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 807 to the basestation 72.

The user equipment 71 executes the reception process as follows. Theradio signal from the base station 72 is received through the antenna807. The received signal is converted from a radio reception frequencyinto a baseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data is passedto a decoding unit 809 and is subjected to a decoding process such aserror correction. Among the pieces of decoded data, the control data ispassed to the protocol processing unit 801, while the user data ispassed to the application unit 802. A series of processes of the userequipment 71 is controlled by a control unit 810. This means that,though not shown in FIG. 8, the control unit 810 is connected to therespective units 801 to 809.

FIG. 9 is a block diagram showing the configuration of the base station72 of FIG. 7 being a base station according to the present invention.The transmission process of the base station 72 shown in FIG. 9 will bedescribed. An EPC communication unit 901 performs data transmission andreception between the base station 72 and the EPC (such as MME unit 73and HeNBGW 74). A communication with another base station unit 902performs data transmission and reception to and from another basestation. The EPC communication unit 901 and the communication withanother base station unit 902 each transmit and receive information toand from a protocol processing unit 903. The control data from theprotocol processing unit 903, and the user data and control data fromthe EPC communication unit 901 and the communication with another basestation unit 902 are stored in a transmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is passed to anencoding unit 905 and is then subjected to an encoding process such aserror correction. There may exist the data output from the transmissiondata buffer unit 904 directly to a modulating unit 906 without theencoding process. The encoded data is modulated by the modulating unit906. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 907 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 908 to one or aplurality of user equipments 71.

The reception process of the base station 72 is executed as follows. Aradio signal from one or a plurality of user equipments 71 is receivedthrough the antenna 908. The received signal is converted from a radioreception frequency into a baseband signal by the frequency convertingunit 907, and is then demodulated by a demodulating unit 909. Thedemodulated data is passed to a decoding unit 910 and is then subjectedto a decoding process such as error correction. Among the pieces ofdecoded data, the control data is passed to the protocol processing unit903, the EPC communication unit 901, or the communication with anotherbase station unit 902, while the user data is passed to the EPCcommunication unit 901 and the communication with another base stationunit 902. A series of processes by the base station 72 is controlled bya control unit 911. This means that, though not shown in FIG. 9, thecontrol unit 911 is connected to the respective units 901 to 910.

Described below are the functions of the Home-eNB 72-2 currently underdiscussion in 3GPP (see Chapter 4.6.2 of Non-Patent Document 1). TheHome-eNB 72-2 has the same function as that of the eNB 72-1. Inaddition, the Home-eNB 72-2 has the function of discovering a suitableserving HeNBGW 74 in the case of connection to the HeNBGW 74. TheHome-eNB 72-2 is connected only to one HeNBGW 74. In other words, in thecase of the connection to the HeNBGW 74, the Home-eNB 72-2 does not usethe Flex function in the S1 interface. When the Home-eNB 72-2 isconnected to one HeNBGW 74, it is not simultaneously connected toanother HeNBGW 74 or another MME unit 73.

The tracking area code (TAC) and PLMN ID of the Home-eNB 72-2 aresupported by the HeNBGW 74. When the Home-eNB 72-2 is connected to theHeNBGW 74, selection of the MME unit 73 at “UE attachment” is performedby the HeNBGW 74 instead of by the Home-eNB 72-2. The Home-eNB 72-2 maybe deployed without network planning. In this case, the Horne-eNB 72-2is moved from one geographical area to another geographical area. TheHome-eNB 72-2 in this case is accordingly required to be connected to adifferent HeNBGW 74 depending on its location.

FIG. 10 is a block diagram showing the configuration of the MMEaccording to the present invention. FIG. 10 shows the configuration ofan MME 73 a included in the MME unit 73 shown in FIG. 7 described above.A PDN GW communication unit 1001 performs data transmission andreception between the MME 73 a and a PDN GW. A base stationcommunication unit 1002 performs data transmission and reception betweenthe MME 73 a and the base station 72 by means of the S1 interface. Ifthe data received from the PDN GW is user data, the user data is passedfrom the PDN GW communication unit 1001 to the base stationcommunication unit 1002 via a user plane communication unit 1003 and isthen transmitted to one or a plurality of base stations 72. If the datareceived from the base station 72 is user data, the user data is passedfrom the base station communication unit 1002 to the PDN GWcommunication unit 1001 via the user plane communication unit 1003 andis then transmitted to the PDN GW.

If the data received from the PDN GW is control data, the control datais passed from the PDN GW communication unit 1001 to a control planecontrol unit 1005. If the data received from the base station 72 iscontrol data, the control data is passed from the base stationcommunication unit 1002 to the control plane control unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission and receptionbetween the MME 73 a and the HeNBGW 74 by means of the interface (IF)according to an information type. The control data received from theHeNBGW communication unit 1004 is passed from the HeNBGW communicationunit 1004 to the control plane control unit 1005. The processing resultsof the control plane control unit 1005 are transmitted to the PDN GW viathe PDN GW communication unit 1001. The processing results of thecontrol plane control unit 1005 are transmitted to one or a plurality ofbase stations 72 by means of the S1 interface via the base stationcommunication unit 1002, and are transmitted to one or a plurality ofHeNBGWs 74 via the HeNBGW communication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2, an idle state mobility managing unit1005-3, or other unit, and performs an overall process for the controlplane. The NAS security unit 1005-1 provides, for example, security of anon-access stratum (NAS) message. The SAE bearer control unit 1005-2manages, for example, a system architecture evolution (SAE) bearer. Theidle state mobility managing unit 1005-3 performs, for example, mobilitymanagement of an idle state (LTE-IDLE state, which is merely referred toas idle as well), generation and control of a paging signal in the idlestate, addition, deletion, update, and search of a tracking area of oneor a plurality of user equipments 71 being served thereby, and trackingarea list management.

The MME 73 a begins a paging protocol by transmitting a paging messageto the cell belonging to a tracking area in which the UE is registered.The idle state mobility managing unit 1005-3 may manage the CSG of theHome-eNBs 72-2 to be connected to the MME 73 a, CSG-IDs, and awhitelist.

In the CSG-ID management, the relationship between a user equipmentcorresponding to the CSG-ID and the CSG cell is managed (for example,added, deleted, updated, or searched). For example, the relationship maybe the relationship between one or a plurality of user equipments whoseuser access registration has been performed with a CSG-ID and the CSGcells belonging to this CSG-ID. In the whitelist management, therelationship between the user equipment and the CSG-ID is managed (forexample, added, deleted, updated, or searched). As an example, thewhitelist may store one or a plurality of CSG-IDs with which userregistration has been performed by a user equipment. The above-mentionedmanagement related to the CSG may be performed by another part of theMME 73 a. A series of processes by the MME 73 a is controlled by acontrol unit 1006. This means that, though not shown in FIG. 10, thecontrol unit 1006 is connected to the respective units 1001 to 1005.

Described below is the function of the MME 73 a currently underdiscussion of 3GPP (see Chapter 4.6.2 of Non-Patent Document 1). The MME73 a performs access control for one or a plurality of user equipmentsbeing members of closed subscriber groups (CSGs). The MME 73 arecognizes the execution of paging optimization as an option.

FIG. 11 is a block diagram showing the configuration of the HeNBGW 74 ofFIG. 7 being a HeNBGW according to the present invention. An EPCcommunication unit 1101 performs data transmission and reception betweenthe HeNBGW 74 and the MME 73 a by means of the S1 interface. A basestation communication unit 1102 performs data transmission and receptionbetween the HeNBGW 74 and the Home-eNB 72-2 by means of the S1interface. A location processing unit 1103 performs the process oftransmitting, to a plurality of Home-eNBs 72-2, the registrationinformation or the like of the data transmitted from the MME 73 a viathe EPC communication unit 1101. The data processed by the locationprocessing unit 1103 is passed to the base station communication unit1102 and is passed to one or a plurality of Home-eNBs 72-2 through theS1 interface.

The data only caused to pass through (to be transparent) withoutrequiring the process by the location processing unit 1103 is passedfrom the EPC communication unit 1101 to the base station communicationunit 1102, and is transmitted to one or a plurality of Home-eNBs 72-2through the S1 interface. A series of processes by the HeNBGW 74 iscontrolled by a control unit 1104. This means that, though not shown inFIG. 11, the control unit 1104 is connected to the respective units 1101to 1103.

Described below is the function of the HeNBGW 74 currently underdiscussion of 3GPP (see Chapter 4.6.2 of Non-Patent Document 1). TheHeNBGW 74 relays an S1 application. The HeNBGW 74 terminates the S1application that is not associated with the user equipment 71 though itis a part of the procedures toward the Home-eNB 72-2 and towards the MME73 a. When the HeNBGW 74 is deployed, the procedure that is notassociated with the user equipment 71 is communicated between theHome-eNB 72-2 and the HeNBGW 74 and between the HeNBGW 74 and the MME 73a. The X2 interface is not established between the HeNBGW 74 and anothernode. The HeNBGW 74 recognizes the execution of paging optimization asan option.

An example of a cell search method in a mobile communication system willbe described next. FIG. 12 is a flowchart showing an outline from a cellsearch to an idle state operation performed by a user equipment (UE) inthe LTE communication system. When starting a cell search, in StepST1201, the user equipment synchronizes slot timing and frame timing bya primary synchronization signal (P-SS) and a secondary synchronizationsignal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as a synchronizationsignal (SS). Synchronization codes, which individually correspond tophysical cell identities (PCIs) assigned per cell, are assigned to thesynchronization signal (SS). The number of PCIs is currently studied in504 ways. The 504 ways of PCIs are used for synchronization, and thePCIs of the synchronized cells are detected (specified).

In Step ST1202, next, the user equipment detects a cell-specificreference signal (CRS) being a reference signal (RS) transmitted fromthe base station per cell and measures the reference signal receivedpower (RSRP). The codes individually corresponding to the PCIs are usedfor the reference signal RS. Separation from another cell is enabled bycorrelation using the code. The code for RS of the cell is derived fromthe PCI specified in Step ST1201, which makes it possible to detect theRS and measure the RS received power.

In Step ST1203, next, the user equipment selects the cell having thebest RS reception quality, for example, the cell having the highest RSreceived power, that is, the best cell, from one or more cells that havebeen detected up to Step ST1202.

In Step ST1204, next, the user equipment receives the PBCH of the bestcell and obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas transmission bandwidth configuration (dl-bandwidth)), the number oftransmission antennas, and system frame number (SFN).

In Step ST1205, next, the user equipment receives the DL-SCH of the cellon the basis of the cell configuration information of the MIB, tothereby obtain a system information block (SIB) 1 of the broadcastinformation BCCH. The SIB1 contains the information about the access tothe cell, information about cell selection, and scheduling informationon other SIB (SIBk; k is an integer equal to or larger than two). Inaddition, the SIB1 contains a tracking area code (TAC).

In Step ST1206, next, the user equipment compares the TAC of the SIB1received in Step ST1205 with the TAC portion of a tracking area identity(TAI) in the tracking area list that has already been possessed by theuser equipment. The tracking area list is also referred to as a TAIlist. TAI is a TA identity and is composed of a mobile country code(MCC), a mobile network code (MNC), and a tracking area code (TAC). MCCis a country code. MNC is a network code. TAC is the code number of atracking area.

If the TAC received in Step ST1205 is identical to the TAC included inthe tracking area list as a result of the comparison of Step ST1206, theuser equipment enters an idle state operation in the cell. If the TACreceived in Step ST1205 is not included in the tracking area list as aresult of the comparison, the user equipment requires a core network(EPC) including MME and the like to change a tracking area through thecell for performing tracking area update (TAU).

The core network updates the tracking area list on the basis of anidentification number (such as a UE-ID) of the user equipmenttransmitted from the user equipment together with a TAU request signal.The core network transmits the updated tracking area list to the userequipment. The user equipment rewrites (updates) the TAC list of theuser equipment on the basis of the received tracking area list. Afterthat, the user equipment enters the idle state operation in the cell.

In the LTE, LTE-A, and universal mobile telecommunication system (UMTS),the introduction of a closed subscriber group (CSG) cell is studied. Asdescribed above, access is allowed for only one or a plurality of userequipments registered with the CSG cell. A CSG cell and one or aplurality of user equipments registered with the CSG cell constitute oneCSG. A specific identification number referred to as CSG-ID is added tothe thus constituted CSG. One CSG may include a plurality of CSG cells.After being registered with any one of the CSG cells, the user equipmentcan access another CSG cell of the CSG to which the registered CSG cellbelongs.

Alternatively, the Home-eNB in the LTE and LTE-A and the Home-NB in theUMTS are used as CSG cells in some cases. The user equipment registeredwith the CSG cell has a whitelist. Specifically, the whitelist is storedin a subscriber identity module (SIM) or USIM. The whitelist stores theCSG information of the CSG cell with which the user equipment has beenregistered. Specifically, the CSG information may be CSG-ID, trackingarea identity (TAD, or TAC. Any one of the CSG-ID and TAC is adequate aslong as they are associated with each other. Alternatively, ECGI isadequate as long as the CSG-ID and TAC are associated with ECGI.

As can be seen from the above, the user equipment that has no whitelist(including a case where the whitelist is empty in the present invention)is not allowed to access the CSG cell but is allowed to access thenon-CSG cell only. On the other hand, the user equipment that has awhitelist is allowed to access the CSG cell of the CSG-ID with whichregistration has been performed as well as the non-CSG cell.

The HeNB and HNB are required to support various services. For example,in certain service, an operator causes the predetermined HeNB and HNB toregister user equipments therein and permits only the registered userequipments to access the cells of the HeNB and HNB, increasing radioresources available for the user equipments, which enables high-speedcommunication. The operator correspondingly sets a high charge comparedwith a normal service.

In order to achieve the above-mentioned service, the closed subscribergroup (CSG) cell accessible only to the registered (subscribed ormember) user equipments is introduced. A large number of closedsubscriber group (CSG) cells are required to be installed in shoppingmalls, apartment buildings, schools, companies, and the like. Forexample, the following manner of use is required: the CSG cells areinstalled for each store in shopping malls, for each room in apartmentbuildings, for each classroom in schools, and for each section incompanies such that only the users who have registered with therespective CSG cells are permitted to use those CSG cells.

The HeNB/HNB is required not only to complement the communicationoutside the coverage of the macro cell (area complementing HeNB/HNB) butalso to support various services as described above (service providingHeNB/HNB). As a result, the HeNB/HNB is installed within the coverage ofthe macro cell in some cases.

Widespread use of smartphones and tablet terminals explosively increasestraffic in cellular radio communications, causing a fear of insufficientradio resources all over the world. To increase spectral efficiency,accordingly, it is studied to downsize cells for further spatialseparation.

FIG. 13 shows the concept of the configuration of conventional cells. Amacro eNB (macro cell) constitutes a relatively-wide-range area coverage1301. Conventionally, relatively-wide-range coverages configured by aplurality of macro eNBs (macro cells) cover an area.

FIG. 14 shows the concept of the configuration of downsized cells. Thesmall eNB (small cell) constitutes a relatively-narrow-range coverage1302 compared with the coverage 1301 of the macro eNB (macro cell).Thus, in order to cover an area as in the conventional case, a largernumber of small eNBs (small cells) than the macro eNBs (macro cells) arerequired.

FIG. 15 shows the concept of the configuration of cells in which macroeNBs (macro cells) and small eNBs (small cells) coexist. The macro eNB(macro cell) constitutes a relatively-wide-range coverage 1303. Thesmall eNB (small cell) constitutes a relatively-narrow-range coverage1304 compared with the coverage 1303 of the macro eNB (macro cell). FIG.15 also shows the case where the coverage of an eNB (cell) is includedin the coverage of another eNB (cell).

In the configuration of cells shown in FIG. 15, the coverage 1303 of themacro eNB (macro cell) and the coverage 1304 of the small eNB (smallcell) may overlap each other in a complicated manner. Or, the coverage1303 of the macro eNB (macro cell) and a coverage 1307 of the small eNB(small cell) may not overlap each other. Further, a large number ofsmall eNBs (small cells) may be configured in the coverage of one macroeNB (macro cell).

The problem solved in the first embodiment will be described below withreference to FIG. 15. The place within the coverage 1303 constituted bythe macro eNB (macro cell), such as the place of the small cell 1305,and the place outside the coverage 1303 of the macro cell, such as theplace of the small cell 1306, are both studied as the places in which asmall cell is installed.

Herein, the macro cell refers to a cell constituting arelatively-wide-range coverage, that is, a cell having a relatively widecoverage area, whereas the macro eNB refers to an eNB constituting themacro cell. The macro eNB may be, for example, a “wide area basestation” (see TS 36.141 V11.1.0 by 3GPP (hereinafter, referred to as“Non-Patent Document 11”)). The macro eNB corresponds to a large-scalebase station device.

The small cell refers to a cell constituting a relatively-narrow-rangecoverage, that is, a cell having a relatively narrow coverage area,whereas the small eNB refers to an eNB constituting a small cell. Thesmall eNB may be, for example, a low power node, local area node, orhotspot. Alternatively, the small eNB may be a pico eNB constituting apico cell, a femto eNB constituting a femto cell, HeNB, RRH, RRU, RRE,or RN. Still alternatively, the small eNB may be a “local area basestation” or “home base station” (see Non-Patent Document 11). The smalleNB corresponds to a small-scale base station device.

A standalone mode, in which a small cell operates similarly to a macrocell, and a macro support mode, in which a small cell operates inassociation with or in coordination with a macro cell, are studied asthe operation modes of small cells. The following two, (1) and (2), willbe disclosed as specific examples of the macro support mode.

(1) 3GPP has proposed control/user data plane split (C/U plane split)and multi-stream as the method of performing communication using aplurality of cells without establishing a plurality of RRC connections(see RWS-120010 by 3GPP (hereinafter, referred to as “Non-PatentDocument 12”) and RWS-120006 by 3GPP (hereinafter, referred to as“Non-Patent Document 13”)). It is conceivable that in the control/userdata plane split (C/U plane split), the macro cell transmits andreceives a control plane (C plane) and the small cell transmits andreceives a user data plane (U plane).

(2) 3GPP has discussed additional carrier types (see the report of RANI66BIS meeting by 3GPP (hereinafter, referred to as “Non-Patent Document14”)). Hereinafter, the additional carrier type may be referred to as anew carrier type (NCT). It is studied that an NCT is configured by asmall cell.

It is conceivable that a large number of small cells will be installed.Without any contrivance, an operator needs to configure the large numberof small cells by taking into account an installation place or a modesupported by the small cell per small cell. This results in complicatedoperation and administration for the operator when a small cell isinstalled.

Described below is a solution in the first embodiment. The installedsmall cell notifies the already installed network equipment of its owncapability. The network equipment that has received the capability ofthe installed small cell from the small cell performs, on the smallcell, a configuration suitable for the capability of the small cell. Thenetwork equipment may select a configuration parameter suitable for thecapability of the small cell on the basis of the received capability ofthe small cell to perform a configuration suitable for the capability ofthe small cell. The network equipment corresponds to a network device.

The solution in the first embodiment eliminates the need for an operatorto configure a small cell by taking into account an installation placeor a mode supported by the small cell per small cell every time a smallcell is installed. This avoids operation and administration for theoperator becoming complicated when a small cell is installed.

The solution in the first embodiment will be specifically describedbelow. The following four, (1) to (4), will be disclosed as specificexamples of the already installed network equipment. The MME, OAM, andHeNBGW described below correspond to higher-level devices. Herein, thehigher-level device refers to a device located on the core network siderelative to a base station (eNB).

(1) Base station (eNB).

(2) MME.

(3) Operation administration and maintenance (OAM).

(4) HeNBGW.

When notifying the network equipment of its own capability, the smallcell may also request its own configuration. In other words, the smallcell may notify the network equipment of its own capability and alsorequest the configuration of its own operation mode.

In place of notifying the network equipment of its own capability, thesmall cell may request its own configuration or the configuration of itsown operation mode. When requesting its own configuration, the smallcell may also notify its own capability.

The installed small cell may notify a neighbor eNB (neighbor cell), suchas another small cell or a macro cell, of its own capability. If theneighbor eNB that has been notified of the capability from the smallcell is another small cell, the other small cell may notify its owncapability as a response to the notification.

The installed small cell may notify the network equipment of its owncapability if a predetermined condition is met or may not notify thenetwork equipment of its own capability if a predetermined condition isnot met. The following two, (1) and (2), will be disclosed as specificexamples of the predetermined condition.

(1) A predetermined condition is set to whether a small cell isinstalled in the coverage of another cell. If a small cell is installedin the coverage of another cell, the small cell notifies the networkequipment of its own capability. If a small cell is not installed in thecoverage of another cell, the small cell does not notify the networkequipment of its own capability. If a small cell is not installed in thecoverage of another cell, also, the small cell may start operating inthe standalone mode. This is effectively applied to the case where theoperation in the macro support mode is not achieved if a small cell isnot installed in the coverage of another cell.

As in the specific example (1), by setting a predetermined condition towhether a small cell is installed in the coverage of another cell, aconfiguration suitable for the installation place of a small cell isenabled without an operator. This avoids operator's operation andadministration becoming complicated when a small cell is installed.

(2) A predetermined condition is set to whether a small cell isinstalled in the coverage of a macro cell. The macro cell with a smallcell installed in its own coverage is referred to as a “coverage macrocell.” If a small cell is installed in the coverage of a macro cell, thesmall cell notifies the network equipment of its own capability. If asmall cell is not installed in the coverage of a macro cell, the smallcell does not notify the network equipment of its own capability. If asmall cell is not installed in the coverage of a macro cell, also, thesmall cell may start operating in the standalone mode. This iseffectively applied to the case where the operation in the macro supportmode is not achieved if a small cell is not installed in the coverage ofa macro cell.

As in the specific example (2), by setting a predetermined condition towhether a small cell is installed in the coverage of a macro cell, theconfiguration suitable for the installation place of a small cell isachieved without an operator. This avoids operator's operation andadministration becoming complicated when a small cell is installed.

Disclosed below is a specific example of the method of judging whether asmall cell is installed in the coverage of another cell or a macro cell.The small cell performs cell search (neighbor cell search) to judgewhether a cell having reception quality not less than a predeterminedthreshold is present. One specific example of the reception quality isRS received power. If judging that a cell having reception quality notless than a predetermined threshold is present, the small cell judgesthat it is installed in the coverage of another cell or a macro cell. Ifjudging that no cell having reception quality not less than apredetermined threshold is present, the small cell judges that it is notinstalled in the coverage of another cell or a macro cell.

If a small cell is installed in the coverage of a macro cell in thespecific example (2) of the predetermined condition, the small cell maynotify the coverage macro cell of its own capability. It is conceivablethat when a small cell operates in the macro support mode, a macro celloperating in association with or in coordination with the small cellwill serve as a coverage macro cell. In that case, the small cellnotifying the coverage macro cell of its own capability means that inoperating in the macro support mode, the small cell notifies a macrocell operating, for example, in association with the small cell of itsown capability. The macro cell, which has received the capability of thesmall cell and operates, for example, in association with the small celloperating in the macro support mode, can perform a configurationsuitable for the capability of the small cell on the small cell. Thisenables a communication system capable of further smooth operation andadministration in the case where a small cell operates in the macrosupport mode.

In the following description, the operation in which a small cellnotifies its own capability may be referred to as a “capabilitynotifying operation.”

The following four, (1) to (4), will be disclosed as specific examplesof the capability notifying operation when a plurality of coverage macrocells are present for a small cell.

(1) A small cell notifies a coverage macro cell, which has the highestreception quality obtained through cell search by the small cell, ofcapability.

(2) A small cell notifies all coverage macro cells of capability. Inthis case, which coverage macro cell is to perform a configurationsuitable for the capability of the small cell is adjusted among thecoverage macro cells that have received the capability.

(3) A higher-level device notifies a small cell of the number ofcoverage macro cells being capability notification destinations. Thesmall cell notifies coverage macro cells not greater than this number ofcapability. The small cell may notify the coverage macro cells havinghigher reception qualities in order.

(4) A higher-level device notifies a small cell of a coverage macro cellbeing a capability notification destination. The small cell notifies thecoverage macro cell of capability.

Disclosed below is a specific example of the method in which a smallcell judges whether a target cell is a macro cell in cell search. Thecell broadcasts an indicator as to whether a target cell is a macrocell. As a result of cell search, the small cell receives the broadcastinformation of a cell having reception quality not less than apredetermined threshold, thereby checking an indicator as to whether atarget cell is a macro cell.

The cell may broadcast an indicator as to whether it supports the macrosupport mode. As a result of cell search, the small cell receives thebroadcast information of a cell having reception quality not less than apredetermined threshold, thereby checking an indicator as to whether thecell supports the macro cell support mode. In the present invention, themacro cell which has a small cell installed in its own coverage and alsosupports the macro support mode, may be a “coverage macro cell.” This isbecause even a macro cell with a small cell installed in its owncoverage cannot support the operation of the small cell in associationwith or in coordination with the macro cell if the macro cell does notsupport the macro support mode.

The small cell notifies network equipment of capability informationindicating its own capability, for example, a capability parameterindicating its own capability, thereby notifying the network equipmentof its own capability. The following seven, (1) to (7), will bedisclosed as specific examples of the capability (capability parameter)of a small cell that is notified to the network equipment by the smallcell.

(1) Indication that a cell is a small cell. This allows the alreadyinstalled network equipment to recognize that a newly installed cell isa small cell without an operator.

(2) Information on a mode to be supported. Examples of the mode includethe standalone mode and the macro support. The macro support mode isclassified into the following modes: (2-1) control/user data plane split(C/U plane split) mode and (2-2) NCT mode. For the (2-2) NCT mode, anyone or all of the seven capability parameters, (2-2-1) to (2-2-7) below,may be further notified: (2-2-1) whether carrier aggregation is enabled,(2-2-2) whether a radio resource of a small cell and a radio resource ofanother cell can be aggregated (referred to as “cell aggregation”),(2-2-3) a bandwidth for enabling transmission and reception, (2-2-4) afrequency band for enabling transmission and reception, (2-2-5) thenumber of CCs or the number of cells that can be supported, (2-2-6) acarrier frequency for enabling transmission and reception, and (2-2-7) aCRS mapping location. This specific example (2) allows the alreadyinstalled network equipment to obtain the information on a mode to besupported by a newly installed small cell without an operator.

(3) Cell identification information of a coverage cell detected in cellsearch by the small cell. Specific examples of the cell identificationinformation include PCI and cell global identifier (CGI). The specificexample (3) simplifies, in the case where the already installed networkequipment causes a newly installed small cell to operate in the macrosupport mode, the selection of a macro cell to be operated togetherwithout an operator. Also, the already installed network equipment canobtain information on the radio environment in the place where a smallcell is actually installed, allowing for the selection of a moresuitable cell as a macro cell to be operated together.

(4) Reception quality of (3) above.

(5) Information on the installation place of the small cell (locationinformation).

(6) Transmission power, which may be the rank of a base station. Thisallows the already installed network equipment to predict the size ofthe coverage of a newly installed small cell without an operator.

(7) Combination of (1) to (6) above.

The following four, (1) to (4), will be disclosed as specific examplesof the interface to be used in notification of capability from a smallcell to network equipment.

(1) Examples of the interface in the case where the network equipment isa base station include an X2 interface and an S1 interface via an MME. Asimilar interface can be used also in the case where a small cellnotifies a neighbor eNB (neighbor cell) of its own capability.

(2) An example interface in the case where the network equipment is anMME is an S1 interface.

(3) An example interface in the case where the network equipment isHeNBGW is an S1 interface.

(4) A new interface may be provided.

The following two, (1) and (2), will be disclosed as specific examplesof the notification method in the case where an X2 interface is used inthe notification of capability from a small cell to network equipment.

(1) New signaling is provided.

(2) A new parameter is added to an “X2 SETUP REQUEST” message (seeChapter 9.1.2.3 of TS 36.423 V11.3.0 by 3GPP (hereinafter, referred toas “Non-Patent Document 15”)) being the existing signaling, and themessage is notified. The “X2 SETUP REQUEST” message is a message usedwhen an eNB transmits initial information to a neighbor eNB. Thus, asmall cell notifies its own capability in the “X2 SETUP REQUEST”message, and can accordingly transmit and receive similar parameters inone operation. This avoids a communication system becoming morecomplicated.

The following two, (1) and (2), will be disclosed as specific examplesof the notification method in the case where an S1 interface is used inthe notification of capability from a small cell to network equipment.

(1) New signaling is provided.

(2) A new parameter is added to the “S1 SETUP REQUEST” message (seeChapter 9.1.8.4 of TS 36.413 V11.2.0 by 3GPP (hereinafter, referred toas “Non-Patent Document 16”)) being the existing signaling, and themessage is notified. The “S1 SETUP REQUEST” message is a message usedwhen an eNB transmits initial information to the MME. Thus, a small cellnotifies its own capability in the “S1 SETUP REQUEST” message, and canaccordingly transmit and receive similar parameters in one operation.This avoids a communication system becoming more complicated.

The following five, (1) to (5), will be disclosed as specific examplesof the configuration parameter in the case where the network equipmentperforms, on a small cell, a configuration suitable for the cability ofthe small cell.

(1) From among the modes supported by a small cell, a suitable mode isconfigured. In other words, an operation mode of the small cell, whichis selected from among the modes supported by the small cell, isconfigured. As a specific example, the type, the standalone mode or themacro support mode, is configured. As a specific example of the methodof selecting an operation mode, the standalone mode is selected for ahigher processing load of the coverage macro cell, whereas the macrosupport mode is selected for a lower processing load of the coveragemacro cell.

The following five, (1-1) to (1-5), will be disclosed as specificexamples of the configuration parameter in the case where the macrosupport mode is configured.

(1-1) The type of an operation mode in the macro support mode. Aspecific example is a control/user data plane split (C/U plane split)mode or an NCT mode. If a small cell supports the macro support modeother than the modes above, the type of the corresponding operation modemay be selected and configured. Alternatively, for example, theconfigurations of the control/user data plane split (C/U plane split)mode and the NCT mode may be enabled.

(1-2) Identification information of a macro cell to be operatedtogether. The following two, (1-2-1) and (1-2-2), will be disclosed asspecific examples of the macro cell to be operated together.

(1-2-1) A coverage macro cell or, among coverage macro cells for a smallcell, a coverage macro cell (also referred to as a “first coverage macrocell”) having the best reception quality in cell search when a smallcell is installed.

(1-2-2) A cell that performs scheduling of resources of the small cellfor the UE (also referred to as a “cell being a scheduling entity”), acell that performs scheduling of performing cross-carrier scheduling fora small cell (also referred to as a “cell being a scheduling entity”),or a cell for which a UE that performs transmission and reception usingthe resource of a small cell monitors PDCCH (also referred to as a “cellbeing a scheduling entity”).

Disclosed below are specific examples of the macro cell to be operatedtogether when the operation mode in the macro support mode is thecontrol/user data plane split (C/U plane split) mode. Herein, the cellthat transmits and receives a control plane to and from the UE, to andfrom which a small cell transmits and receives user data plane, is amacro cell to be operated together. Examples of such a macro cellinclude a coverage macro cell and a first coverage macro cell.

Specific examples of the macro cell to be operated together when theoperation mode in the macro support mode is the NCT mode will bedisclosed below. Herein, among the cells that are subjected to cellaggregation by the UE, the cell that performs scheduling of resources ofthe small cell for the UE (also referred to as a “cell being ascheduling entity”) is a macro cell to be operated together. Or, thecell that performs scheduling of performing cross-carrier scheduling fora small cell (also referred to as a “cell being a scheduling entity”) isa macro cell to be operated together. Or, the cell for which the UE thatperforms transmission and reception using the resource of a small cellmonitors PDCCH (also referred to as a “cell being a scheduling entity”)is a macro cell to be operated together.

The cell being a scheduling entity is, for example, a coverage macrocell for a small cell. Further, the cell being a scheduling entity is afirst coverage macro cell.

(1-3) Carrier frequency.

(1-4) Bandwidth.

(1-5) Frequency band.

(2) Energy saving (ES) policy, which will be specifically disclosed in asecond embodiment.

(3) Carrier frequency of a coverage macro cell.

(4) Identifier of a group to which a small cell belongs (hereinafter,also referred to as a “small cell cluster” or a “small cell group”). Thesmall cell may belong to a plurality of small cell clusters. Or, numbersof the small cells in a small cell cluster may be notified together.This allows for the use of the “identifier of a small cell cluster towhich a small cell belongs” or the “information containing theidentifier of a small cell cluster and numbers of the small cells in asmall cell cluster” as the small cell identification information beingthe information for identifying a small cell, in addition to PCI.

A large number of small cells can be installed in a narrow range. ThePCIs are available in total of 504 types of codes, which are finite.Thus, compared with before the introduction of small cells, there is aconcern of PCIs overlapping after the introduction of small cells. Inoverlapping of PCIs, a cell can be identified using the CGI and theECGI. However, high bit counts of the CGI and ECGI require a largeamount of radio resources to exchange the CGI and ECGI between, forexample, the UE and the eNB, compared with the case where the PCIs areexchanged therebetween.

If the “information containing PCI and the identifier of a small cellcluster to which a small cell belongs” or the “information containingPCI, the identifier of a small cell cluster, and numbers of small cellsin a small cell cluster” requires a low bit count compared with the caseof CGI and ECGI, it is effective to use the “information containing PCIand the identifier of a small cell cluster to which a small cellbelongs” or the “information containing PCI, the identifier of a smallcell cluster, and numbers of small cells in a small cell cluster” as acell identification method when PCIs overlap each other, from theviewpoint of effective use of radio resources. Also, the identificationinformation of small cells belonging to the same small cell cluster maybe notified together.

(5) Combination of (1) to (4) above.

The following five, (1) to (5), will be disclosed as specific examplesof the small cell cluster.

(1) A group of small cells whose scheduling entities are the same. Agroup of small cells whose concentrated control nodes are the same. Forexample, a group of small cells controlled by the same concentratedcontrol node, the same entity engaging in scheduling, or the sameconcentrator in cell aggregation and in CoMP.

(2) A group of small cells according to an installation place. A groupof small cells installed in a specific area. For example, a group ofsmall cells installed in the same station yard or a group of small cellsinstalled in the same school.

(3) A group of small cells having the same ES policy.

(4) A group of small cells belonging to the same CoMP cooperating set.

(5) A group of small cells belonging to the same frequency layer.

Specific examples of the interface used in the notification of aconfiguration from network equipment to a small cell are similar to thespecific examples of the interface used in the notification ofcapability from a small cell to network equipment, which will not bedescribed here.

The following two, (1) and (2), will be disclosed as specific examplesof the notification method in the case where an X2 interface is used inthe notification from network equipment to a small cell.

(1) New signaling is provided.

(2) A new parameter is added to the “X2 SETUP RESPONSE” message beingthe existing signaling (see Chapter 9.1.2.4 of Non-Patent Document 15),and the message is notified. The “X2 SETUP RESPONSE” message is aresponse message used in transmission of initial information from an eNBto a neighbor eNB. Thus, notification of the configuration for a smallcell in the “X2 SETUP RESPONSE” message avoids a communication systembecoming more complicated.

The following two, (1) and (2), will be disclosed as specific examplesof the notification method in the case where an S1 interface is used innotification of capability from a small cell to network equipment.

(1) New signaling is provided.

(2) A new parameter is added to the “S1 SETUP RESPONSE” message beingthe existing signaling (see Chapter 9.1.8.5 of Non-Patent Document 16),and the message is notified. The “S1 SETUP RESPONSE” message is aresponse message used in transmission of initial information from an eNBto an MME. Thus, notification of the configuration for a small cell inthe “S1 SETUP RESPONSE” message avoids a communication system becomingmore complicated.

The following five, (1) to (5), will be disclosed as specific examplesof the operation of a small cell when the small cell receives aconfiguration parameter from network equipment.

(1) A small cell starts operating in a mode that has been configured,that is, an operation mode that has been configured.

(1-1) The case where, for example, the standalone mode is configuredwill be described. In this case, an operation similar to that of anormal cell is performed.

(1-2) The case where, for example, the macro support mode is configuredwill be described.

(1-2-1) A small cell notifies a UE being served thereby that the smallcell is operating in the macro support mode. For example, the small cellnotifies a UE being served thereby that the small cell is a cell onwhich camping (CAMP ON) cannot be performed.

The following two, (1-2-1-a) and (1-2-1-b), will be disclosed asspecific examples of the method in which a small cell notifies a UEbeing served thereby.

(1-2-1-a) Notification is made in broadcast information. This allowsboth of a UE in an idle state (RRC_IDLE) and a UE in a connected state(RRC_CONNECTED) to receive the information.

(1-2-1-b) In broadcast information, “cellBarred” is changed to “barred.”The use of the existing parameter as described above avoids acommunication system becoming more complicated. It is also possible toconstruct a communication system having excellent backwardcompatibility.

(1-2-2) A small cell does not transmit PDCCH.

(1-2-3) A small cell does not transmit paging.

Described below is a specific example of the operation of a small cellwhen the operation mode in the macro support mode is configured to thecontrol/user data plane split (C/U plane split) mode. The operation as auser data plane cell is started. In other words, the operations in anRRC protocol, a PDCP protocol, and an RLC protocol for control planeconnection are stopped.

Described below are specific examples of the operation of a small cellwhen the operation mode in the macro support mode is configured to theNCT mode. The number of CRS mappings is reduced more than in the case ofa normal cell. CRS is transmitted at a mapping location in NCT. PBCH andMIB are not transmitted. PDCCH is not transmitted. A paging message isnot transmitted.

(2) A small cell starts operating in the configured ES policy.

(3) If the carrier frequency of a coverage macro cell is configured, asmall cell notifies a UE being served thereby of the configured carrierfrequency of the coverage macro cell. Specific examples of the method inwhich a small cell notifies a UE being served thereby will be disclosedbelow.

A small cell notifies that the carrier frequency of a coverage macrocell is a frequency with high priority in cell reselection.Specifically, notification is made in an RRC message. Notification ismade in the “RRC Connection Release” message. Or, notification is madein broadcast information. A carrier frequency is configured to afrequency with high “cell Reselection Priority” of the systeminformation in broadcast information (see Chapters 5.2.4.1 and 5.2.4.7of Non-Patent Document 2).

As in the specific example (3), with the small cell notifying a UE beingserved thereby of the carrier frequency of the coverage macro cell, theUE being served by the small cell can preferentially select the coveragemacro cell when a small cell shifts to the ES operation.

(4) A small cell notifies a neighbor cell of a configuration parameter.A small cell may notify another small cell in the same cluster of aconfiguration parameter. The neighbor cell may be a cell judged to havethe reception quality not less than a predetermined threshold in cellsearch performed by a small cell. An X2 interface can be used in thenotification of a configuration parameter. Specific examples of thenotification method in the case where an X2 interface is used aresimilar to the specific examples of the above-mentioned notificationmethod in the case where an X2 interface is used in the notification ofcapability from a small cell to network equipment, which will not bedescribed here.

(5) Combination of (1) to (4) above.

Next, a specific example of the sequence of a communication system inthe case where the solution of the first embodiment is used will bedescribed with reference to FIGS. 16 and 17. FIGS. 16 and 17 show anexample sequence of the communication system in the first embodiment.FIG. 16 is continuous with FIG. 17 at a boundary BL1.

In Step ST1401, a small cell is installed. In Step ST1402, the smallcell performs neighbor cell search.

In Step ST1403, the small cell judges whether it is installed in thecoverage of a macro cell, thereby judging whether a coverage macro cellis present. If judging that it is installed in the coverage of a macrocell, the small cell judges that a coverage macro cell is present andthen moves to Step ST1404. If judging that it is not installed in thecoverage of a macro cell, the small cell judges that no coverage macrocell is present and then moves to Step ST1411.

In Steps ST1404 and ST1405, the small cell notifies neighbor cellsincluding the coverage macro cell of its own capability. Specifically,the small cell notifies the coverage macro cell of its own capability inStep ST1404 and notifies the neighbor cell other than the coverage macrocell of its own capability in Step ST1405.

In Step ST1406, the coverage macro cell that has received the capabilityof the small cell in Step ST1404 selects a configuration suitable forthe capability of the small cell. Specifically, the coverage macro cellselects a configuration parameter suitable for the capability of thesmall cell.

In Step ST1407, the coverage macro cell notifies the small cell of theconfiguration parameter selected in Step ST1406.

In Step ST1408, the small cell judges whether the configurationparameter received in Step ST1407 contains the carrier frequency of thecoverage macro cell. If judging that the configuration parametercontains the carrier frequency of the coverage macro cell, the smallcell moves to Step ST1409. If judging that the configuration parameterdoes not contain the carrier frequency of the coverage macro cell, thesmall cell moves to Step ST1410.

In Step ST1409, the small cell notifies a UE being served thereby of thecarrier frequency of the coverage macro cell contained in theconfiguration parameter received in Step ST1407. The following three,(1) to (3), will be disclosed as specific examples of the receptionmethod by a UE being served by the small cell: (1) when the carrierfrequency of the coverage macro cell is mapped to the RRC message, inreception of an RRC message, (2) when the carrier frequency of thecoverage macro cell is mapped to the broadcast information, in receptionof broadcast information during cell selection or cell reselection, and(3) when the carrier frequency of the coverage macro cell is mapped tothe broadcast information, in reception of update notification of systeminformation.

In Step ST1410, the small cell judges whether the standalone mode hasbeen configured on the basis of the configuration parameter received inStep ST1407. If judging that the standalone mode has been configured,the small cell moves to Step ST1411. If judging that the standalone modehas not been configured, the small cell moves to Step ST1412. If judgingthat the standalone mode has not been configured, the small cell mayjudge that the macro support mode has been configured and then move toStep ST1412.

In Step ST1411, the small cell starts operating in the standalone mode.

In Step ST1412, the small cell judges whether the control/user dataplane split (C/U plane split) mode has been configured on the basis ofthe configuration parameter received in Step ST1407. If judging that thecontrol/user data plane split (C/U plane split) mode has beenconfigured, the small cell moves to Step ST1414. If judging that thecontrol/user data plane split (C/U plane split) mode has not beenconfigured, the small cell moves to Step ST1413.

In Step ST1413, the small cell judges whether the NCT mode has beenconfigured on the basis of the configuration parameter received in StepST1407. If judging that the NCT mode has been configured, the small cellmoves to Step ST1415. If judging that the NCT mode has not beenconfigured, the small cell ends the process in installation and thenmoves to another process. In the case where the macro support modeincludes another mode in addition to the control/user data plane split(C/U plane split) mode and the NCT mode, however, the operation of thesmall cell is not limited to the above. In other words, the small celljudges whether another mode has been configured, and starts operating inthe other mode if judging that the other mode has been configured, orends the process in installation and then moves to another process ifjudging that the another mode has not been configured. The other processis not characteristic of the present invention, which will not bedescribed here.

In Step ST1414, the small cell starts operating in the control/user dataplane split (C/U plane split) mode. In Step ST1415, the small cellstarts operating in the NCT mode.

The processes of Steps ST1412 to ST1415 are not limited to what isdescribed above when, for example, the control/user data plane split(C/U plane split) mode and the NCT mode can be configured. In otherwords, it is judged whether the control/user data plane split (C/U planesplit) mode and the NCT mode have been configured and, if it is judgedthat the modes have been configured, the operation is started in thecontrol/user data plane split (C/U plane split) mode and the NCT mode.

In Step ST1417, the UE judges whether to perform cell selection or cellreselection. If judging not to perform cell selection or cellreselection, the UE repeats the process of Step ST1417. If judging toperform cell selection or cell reselection, the UE moves to Step ST1418.

In Step ST1418, the UE selects a cell in accordance with broadcastinformation. For example, in the case of having received the carrierfrequency of the coverage macro cell in Step ST1409, the UE performscell search preferentially from the carrier frequency of the coveragemacro cell in cell selection or cell reselection.

The first embodiment achieves the following effects. When a small cellis installed, the small cell can start operating without an operatorirrespective of the installation place of the small cell or the supportmode of the small cell. This achieves easy operation and administrationby the operator when a small cell is installed.

First Modification of First Embodiment

Although the first embodiment has disclosed a small cell cluster,nothing has been disclosed as a result of the discussion in 3GPP as tothe method of managing the small cell cluster disclosed in the firstembodiment. This results in a problem that a unified operation of thecommunication system cannot be achieved. A first modification of thefirst embodiment will therefore disclose the method of managing a smallcell cluster.

The method of managing a small cell cluster includes, for example, thefollowing two steps (1) and (2). Steps (1) and (2) are performed in thestated order. The processes of Steps (1) and (2) can be performedrepeatedly or as needed.

(1) Small cells to be included in a small cell cluster are determined.(2) A list of small cells included in a small cell cluster is stored inthe entity that manages the small cell cluster.

The following six, (1-1) to (1-6), will be disclosed as specificexamples of the method of determining small cells to be included in asmall cell cluster of Step (1).

(1-1) Small cells to be included in a small cell cluster are determinedon the basis of cell aggregation. For example, small cells aredetermined such that a small cell cluster includes small cells whosescheduling entities are the same.

(1-2) Small cells to be included in a small cell cluster are determinedon the basis of an installation place. For example, small cells aredetermined such that a small cell cluster includes small cells installedin the same station yard. Or, for example, small cells are determinedsuch that a small cell cluster includes small cells installed in thecoverage of the same coverage macro cell. Or, for example, small cellsare determined such that a small cell cluster includes small cellsinstalled in the same tracking area (TA).

(1-3) Small cells to be included in a small cell cluster are determinedon the basis of CoMP. For example, small cells are determined such thata small cell cluster includes small cells included in the same CoMPcooperating set.

(1-4) Small cells to be included in a small cell cluster are determinedon the basis of the connected network equipment. For example, smallcells are determined such that a small cell cluster includes small cellsconnected to the same MME. Or, for example, small cells are determinedsuch that a small cell cluster includes small cells connected to thesame HeNBGW.

(1-5) Small cells to be included in a small cell cluster are determinedon the basis of the ES policy. For example, small cells are determinedsuch that a small cell cluster includes small cells having the same ESpolicy. Or, for example, small cells are determined such that a smallcell cluster includes small cells expected to shift from the normaloperation to the energy saving operation at the same timing. Or, forexample, small cells are determined such that a small cell clusterincludes small cells expected to shift from the energy saving operationto the normal operation at the same timing.

(1-6) Combination of (1-1) to (1-5) above.

The following six, (2-1) to (2-6), will be disclosed as specificexamples of the entity that manages a small cell cluster that stores alist of small cells included in a small cell cluster in Step (2).

(2-1) A scheduling entity in cell aggregation. A concentrated controlnode in cell aggregation. This specific example (2-1) is highlycompatible with the specific example (1-1) of the method of determiningsmall cells to be included in a small cell cluster. In other words, bycausing the entity that manages a small cell cluster to be thescheduling entity in cell aggregation, the scheduling entity in cellaggregation is the same as the entity that manages a small cell cluster.This accordingly eliminates the need for exchanging, for example, theinformation on small cells whose scheduling entities are the same,avoiding a communication system becoming more complicated.

(2-2) A concentrated control entity for CoMP (also referred to as a“CoMP concentrator” or a “concentrated control node”). This specificexample (2-2) is highly compatible with the specific example (1-3) ofthe method of determining small cells to be included in a small cellcluster. In other words, by causing the entity that manages a small cellcluster to be a CoMP concentrator, if a set of cells managed by one CoMPconcentrator is a CoMP cooperating set, the entity that manages cellsincluded in a CoMP cooperating set is the same as the entity thatmanages a small cell cluster. This accordingly eliminates the need forexchanging, for example, the information on small cells included in thesame CoMP cooperating set, avoiding a communication system becoming morecomplicated.

(2-3) Operation administration and maintenance (OAM). This specificexample (2-3) is highly compatible with the specific examples (1-2) and(1-5) of the method of determining small cells to be included in a smallcell cluster. If a cell is newly installed, the cell may report itsinstallation place to the OAM. In this case, by causing the entity thatmanages a small cell cluster to be the OAM, the entity that recognizesthe installation place of the cell is the same as the entity thatmanages a small cell cluster. This accordingly eliminates the need forexchanging, for example, the information on an installation place of acell, avoiding a communication system becoming more complicated. The OAMmay configure an ES policy. In this case, by causing the entity thatmanages a small cell cluster to be the OAM, the entity that configuresan ES policy is the same as the entity that manages a small cellcluster. This eliminates the need for exchanging, for example, the ESpolicy information of a cell, avoiding a communication system becomingmore complicated.

(2-4) A coverage macro cell. This specific example (2-4) is highlycompatible with the specific example (1-2) of the method of determiningsmall cells to be included in a small cell cluster in the case wheresmall cells are determined such that a small cell cluster includes smallcells installed in the same coverage macro. The specific example (2-4)is also highly compatible with the specific example (1-5) of the methodof determining small cells to be included in a small cell cluster. Inother words, by causing the entity that manages a small cell cluster tobe a coverage macro cell, if a coverage macro cell configures an ESpolicy, the entity that configures the ES policy is the same as theentity that manages a small cell cluster. This eliminates the need forexchanging, for example, the ES policy information of a cell, avoiding acommunication system becoming more complicated.

(2-5) MME. This specific example (2-5) is highly compatible with thespecific example (1-2) of the method of determining small cells to beincluded in a small cell cluster in the case where small cells aredetermined such that a small cell cluster includes small cells installedin the same TA. The specific example (2-5) is also highly compatiblewith the specific example (1-4) of the method of determining small cellsto be included in a small cell cluster in the case where small cells aredetermined such that a small cell cluster includes small cells connectedto the same MME. The MME manages a TA. Thus, the entity that recognizessmall cells installed in the same TA is the same as the entity thatmanages a small cell cluster. This eliminates the need for exchanging,for example, the information on small cells installed in the same TA,avoiding a communication system becoming more complicated.

(2-6) HeNBGW. This specific example (2-6) is highly compatible with thespecific example (1-2) of the method of determining small cells to beincluded in a small cell cluster in the case where small cells aredetermined such that a small cell cluster includes small cells installedin the same station yard. This specific example (2-6) is also highlycompatible with the specific example (1-4) of the method of determiningsmall cells to be included in a small cell cluster in the case wheresmall cells are determined such that a small cell cluster includes smallcells connected to the same HeNBGW. For example, this is the case wherea HeNBGW is installed in a station yard and a HeNB in the station yardis connected to the HeNBGW. In such a case, by causing the entity thatmanages a small cell cluster to be a HeNBGW, the entity that recognizessmall cells installed in the same station yard is the same as the entitythat manages a small cell cluster. This accordingly eliminates the needfor exchanging, for example, the information on small cells installed inthe same station yard, avoiding a communication system becoming morecomplicated.

The first modification of the first embodiment achieves the followingeffect. The method of managing a small cell cluster is clarified,achieving a unified operation of a communication system.

Second Embodiment

Described below is a solution solved in the second embodiment. 3GPP hasdiscussed energy saving (ES) of infrastructure. For ES, cells such as asmall cell and a macro cell are configured to switch between a state inwhich a normal operation described below is performed (also referred toas an “active state” or “on-state”) and a state in which an energysaving operation described below is performed (also referred to as a“dormant state” or “off-state”). Herein, the energy saving operationrefers to an operation with reduced consumption energy compared with thenormal operation. In the following description, the operation ofswitching from the on-state to the off-state may be referred to as“switch off,” whereas the operation of switching from the off-state tothe on-state may be referred to as “switch on.”

Described below is the conventional ES policy. In the conventional ESpolicy, a cell switches itself off, specifically, shifts from the normaloperation to the energy saving operation (also referrers to as “shiftsfrom the active state to the dormant state”), by its own judgment. Inswitch-off, a cell notifies a neighbor cell that it is to switch itselfoff. When load increases, the neighbor cell requests switch-on,specifically, a shift from the energy saving operation to the normaloperation (also referred to as “re-activation from the dormant state”)of the cell being switched off (see Non-Patent Document 1).

Non-Patent Document 1 discloses that an operator can configure the ESfunction. The configured information contains the following (1) and (2):(1) the ability of an eNB to perform autonomous cell switch-off, and (2)the ability to re-activate dormant cells owned by a neighbor eNB.

Non-Patent Document 1 also discloses that the OAM configures thefollowing (1) and (2): (1) policies used by the eNB for switch-offdecision, and (2) policies used by neighbor eNBs for requesting there-activation of a dormant cell.

The problem solved in the second embodiment will be described below withreference to FIG. 15. The place within the coverage 1303 configured bythe macro eNB (macro cell), such as the small cell 1305, and the placeoutside the coverage 1303 of the macro cell, such as the small cell1306, are studied as the installation places of small cells.

The standalone mode, in which a small cell operates similarly to a macrocell, and the macro support mode, in which a small cell operates inassociation with or in coordination with a macro cell, are both studiedas the operation modes of small cells.

In the introduction of small cells, one type of ES policy conventionallyemployed may be inappropriate. Described below is a specific example ofsuch an inappropriate case.

Even in the conventional ES policy, for higher load, the neighbor cellcan request switch-on of a cell being switched off. Considered here is acase where a neighbor cell is a coverage macro cell and a large numberof small cells are installed in the coverage macro cell. Suppose thatthe large number of small cells switch themselves off by their ownjudgment as in a conventional case. When its own load becomes higher,the coverage macro cell requests switch-on of the small cell beingswitched off. A large number of small cells are switched off in thiscase, and accordingly, the coverage macro cell requests switch-on of thelarge number of small cells. This increases the processing load of thecoverage macro cell and also increases the information to be transmittedand received.

Described below is a solution in the second embodiment. In the secondembodiment, an ES policy unique to a small cell different from aconventional one is newly provided. This achieves an ES operationoptimum for a communication system in which a small cell is introduced.The following will specifically describe the solution in the secondembodiment.

As described above, Non-Patent Document 1 discloses that the OAMconfigures policies used by the eNB for cell switch-off decision orpolicies used by neighbor eNBs for requesting the re-activation of adormant cell. The “policies for cell switch-off decision” and the“policies for requesting the re-activation of a dormant cell,” however,are merely variations of one type of the conventional ES policy. Onetype of the conventional ES policy is as follows: a cell switches itselfoff, specifically, shifts to the energy saving operation (also referredto as “shifts to the dormant state”), by its own judgment. Inswitch-off, the cell informs a neighbor cell that the cell is to switchitself off. When load becomes higher, the neighbor cell requestsswitch-on, specifically, a shift to the normal operation or reactivationof the cell being switched off (see Non-Patent Document 1).

The following two, (1) and (2), will be disclosed as specific examplesof the ES policy unique to a small cell newly provided in the secondembodiment.

(1) A small cell follows an instruction to permit the cell to switchitself off (hereinafter, also merely referred as “permit switch-off”) orprohibit the cell from switching itself off (hereinafter, also merelyreferred to as “prohibit switch-off”) from another cell. Another cellmay be a concentrated control node for a small cell. Or, another cellmay be an ES concentrated control node (also referred to as an “ESconcentrator”). Or, when it is installed in the coverage of anothercell, the small cell may follow an instruction to permit or prohibitswitch-off from the other cell.

As the ES policy unique to a small cell, a small cell that has beeninstructed to permit switch-off operates as follows. A small cell canswitch itself off by its own judgment. In switch-off, the small cellnotifies a neighbor cell that it is to switch itself off. In notifyingthat is to switch itself off, the small cell may also notify anindicator as to whether it is a small cell. The small cell may alsonotify its own identifier. When requested to switch itself on from aneighbor cell, the small cell switches itself on.

The small cell that has been instructed to prohibit switch-off operatesas follows. The small cell cannot switch itself off by its own judgment.In other words, the small cell does not switch itself off.

The small cell located in the coverage of another cell operates as inthe ES policy unique to a small cell, and the small cell located outsidethe coverage of another cell operates as follows. The small cell canswitch itself off by its own judgment. In switch-off, the small cellnotifies a neighbor cell that it is to switch itself off. In notifyingthat it is to switch itself off, the small cell may also notify anindicator as to whether it is a small cell. Or, the small cell may alsonotify the identifier of its own cell. When requested to switch itselfon from the neighbor cell, the small cell switches itself on.

(2) When installed in the coverage of a macro cell, the small cellfollows an instruction to permit or prohibit switch-off from thecoverage macro cell.

The small cell that has been instructed to permit switch-off operates asfollows. The small cell can switch itself off by its own judgment. Toswitch itself off, the small cell notifies the coverage macro cell thatit is to switch itself off. In notifying that it is to switch itselfoff, the small cell may also notify an indicator as to whether it is asmall cell. The small cell may also notify its own identifier. Whenrequested to switch itself on from the coverage macro cell, the smallcell switches itself on.

The small cell that has been instructed to prohibit switch-off operatesas follows. The small cell cannot switch itself off by its own judgment.In other words, the small cell does not switch itself off.

The small cell located outside the coverage of the macro cell operatesas follows. The small cell can switch itself off by its own judgment. Inswitch-off, the small cell notifies a neighbor cell that it is to switchitself off. In notifying that it is to switch itself off, the small cellmay also notify an indicator as to whether it is a small cell. The smallcell may also notify its own identifier. When requested to switch itselfon from the neighbor cell, the small cell switches itself on.

Specific examples of the method in which a small cell judges whether itis installed in the coverage of another cell or a macro cell are similarto those of the first embodiment, which will not be described here.

Specific examples of the method in which a small cell judges whether atarget cell is a macro cell in cell search are similar to those of thefirst embodiment, which will not be described here.

The following two, (1-1) and (1-2), will be disclosed as specificexamples of the operation in the case where a plurality of cells arepresent in the specific example (1) of the ES policy unique to a smallcell.

(1-1) A small cell follows the instructions from all the other cells.Specifically, the small cell, which has been instructed to permitswitch-off from all the other cells, operates as follows. The small cellcan switch itself off by its own judgment. In switch-off, the small cellnotifies a neighbor cell that it is to switch itself off. When requestedto switch itself on from the neighbor cell, the small cell switchesitself on.

The small cell, which has been instructed to prohibit switch-off from atleast another cell, operates as follows. The small cell cannot switchitself off by its own judgment. In other words, the small cell does notswitch itself off.

(1-2) A small cell follows an instruction of other cell that acts as arepresentative (hereinafter, also referred to as “representative othercell”) among a plurality of other cells. Specifically, the small celldecides the representative other cell.

The small cell, which has been instructed to permit switch-off from therepresentative other cell, operates as follows. The small cell canswitch itself off by its own judgment. In switch-off, the small cellnotifies the representative other cell or a neighbor cell that it is toswitch itself off. When requested to switch itself on from therepresentative other cell or the neighbor cell, the small cell switchesitself on.

The small cell, which has been instructed to prohibit switch-off fromthe representative other cell, operates as follows. The small cellcannot switch itself off by its own judgment. In other words, the smallcell does not switch itself off.

The following three, (1-2-1) to (1-2-3), will be disclosed as specificexamples of the method of determining representative other cell.

(1-2-1) A cell having the highest reception quality in cell search by asmall cell is representative other cell.

(1-2-2) A cell, which has performed a configuration suitable for thecapability of a small cell using the first embodiment, is representativeother cell.

(1-2-3) A cell, which is operated together with a small cell in themacro support mode, is representative other cell. Specific examples ofthe cell to be operated together with a small cell are similar to thoseof the first embodiment, which will not be described here.

The following two, (2-1) and (2-2), will be disclosed as specificexamples of the operation in the case where a plurality of coveragemacro cells are present in the specific example (2) of the ES policyunique to a small cell.

(2-1) The small cell follows the instructions of all the coverage macrocells. Specifically, the small cell, which has been instructed to permitswitch-off from all the coverage macro cells, operates as follows. Thesmall cell can switch itself off by its own judgment. In switch-off, thesmall cell notifies all the coverage macro cells that it is to switchitself off. When requested to switch itself on from the coverage macrocell, the small cell switches itself on.

The small cell, which has been instructed to prohibit switch-off from atleast one coverage macro cell, operates as follows. The small cellcannot switch itself off by its own judgment. In other words, the smallcell does not switch itself off.

(2-2) The small cell follows an instruction of a coverage macro cellthat acts as a representative (hereinafter, also referred to as a“representative coverage macro cell”) among a plurality of coveragemacro cells. Specifically, the small cell determines a representativecoverage macro cell.

The small cell, which has been instructed to permit switch-off from therepresentative coverage macro cell, operates as follows. The small cellcan switch itself off by its own judgment. In switch-off, the small cellnotifies the representative coverage macro cell or the coverage macrocell that it is to switch itself off. When requested to switch itself onfrom the representative coverage macro cell or the coverage macro cell,the small cell switches itself on.

The small cell, which has been instructed to prohibit switch-off fromthe representative coverage macro cell, operates as follows. The smallcell cannot switch itself off by its own judgment. In other words, thesmall cell does not switch itself off.

The following three, (2-2-1) to (2-2-3), will be disclosed as specificexamples of the method of determining a representative coverage macrocell.

(2-2-1) A coverage macro cell having the highest reception quality incell search by a small cell is a representative coverage macro cell. Inother words, the first coverage macro cell is a representative coveragemacro cell.

(2-2-2) A coverage macro cell, which has performed a configurationsuitable for the capability of a small cell using the first embodiment,is a representative coverage macro cell.

(2-2-3) A macro cell to be operated together with a small cell in themacro support mode is a representative coverage macro cell. Specificexamples of the macro cell that is operated together with a small cellare similar to those of the first embodiment, which will not bedescribed here.

The following three, (1) to (3), will be disclosed as specific examplesof the entity that configures whether to use the ES policy unique to asmall cell and of the method of configuring whether to use the ES policyunique to a small cell in the small cell (referred to as a “method ofconfiguring an ES policy”).

(1) Determination is made statically. The small cell uses the ES policyunique to a small cell. This eliminates the need for the configurationas to whether to use the ES policy unique to a small cell and thejudgment as to whether to use the ES policy unique to a small cell inthe small cell. Unlike specific examples (2) and (3) described below,configuration processing is not required, and signaling forconfiguration or the like is not required, avoiding a communicationsystem becoming more complicated.

(2) A small cell per se configures whether to use the ES policy uniqueto a small cell. Configuring by the small cell per se eliminates theneed for judging whether to use the ES policy in the small cell. Thefollowing two, (2-1) and (2-2), will be disclosed as specific examplesin that case.

(2-1) If a small cell is installed in the coverage of another cell, thatis, if a small cell has a coverage cell, the small cell configures touse the ES policy unique to a small cell. If a small cell is notinstalled in the coverage of another cell, that is, if a small cell hasno coverage cell, the small cell configures to use no ES policy uniqueto a small cell. Or, a small cell may configure to use the conventionalES policy.

(2-2) If a small cell is installed in the coverage of a macro cell, thatis, if a small cell has a coverage macro cell, the small cell configuresto use the ES policy unique to a small cell. If a small cell is notinstalled in the coverage of a macro cell, that is, if a small cell hasno coverage macro cell, the small cell configures to use no ES policyunique to a small cell. For example, a small cell may use theconventional ES policy.

(3) As in the first embodiment, the already installed network equipmentconfigures whether to use the ES policy unique to a small cell. Thenetwork equipment performs a configuration using the configurationparameter suitable for the capability of the small cell, which isnotified from the network equipment to the small cell when a small cellis installed. Specifically, the network equipment performs aconfiguration using the energy saving (ES) policy being a configurationparameter. If there is no energy saving (ES) policy being aconfiguration parameter, a configuration may be made such that the ESpolicy unique to a small cell is not used. Or, if there is no ES policybeing a configuration parameter, a configuration may be made such thatthe conventional ES policy is used. The already installed networkequipment may judge whether to use the ES policy unique to a small cell.Specific examples of the already installed network equipment include anES concentrator in addition to the specific examples of the firstembodiment. If the entity that judges whether to use the ES policyunique to a small cell differs from the entity that configures whetherto use the ES policy unique to a small cell, the judgment entity maynotify the configuration entity of the information as to whether to usethe ES policy unique to a small cell. The small cell may judge whetherto use the ES policy unique to a small cell on the basis of theconfiguration parameter notified from the network equipment being aconfiguration entity.

Disclosed below are specific examples of the method in which anothercell (such as a coverage cell, a coverage macro cell, or a neighborcell), which notifies a small cell that it is to “permit switch-off” or“prohibit switch-off,” recognizes whether a target cell uses the ESpolicy unique to a small cell, per specific example of the method ofconfiguring an ES policy.

The following two, (1-1) and (1-2), will be disclosed as specificexamples of the case where the method of configuring an ES policy (1) isused.

(1-1) A small cell broadcasts that it is a small cell. Another cellreceives the broadcast information of a target cell to check whether itis a small cell.

(1-2) When a small cell is installed using the first embodiment,judgment is made on the basis of the capability parameter of the smallcell, which is notified from the small cell. When the capabilityparameter includes an indication that a target cell is a small cell, thetarget cell is judged to be a small cell. Alternatively, the cell thathas notified its own capability parameter may be judged to be a smallcell.

The following (2-1) will be disclosed as a specific example of the casewhere the method of configuring an ES policy (2) is used.

(2-1) The specific example (4) of the operation of the small cell whenit receives a configuration parameter from network equipment, disclosedin the first embodiment, is used.

The following two, (3-1) and (3-2), will be disclosed as specificexamples of the case where the method of configuring an ES policy (3) isused.

(3-1) As in (2-1) above, the specific example (4) of the operation of asmall cell when it receives a configuration parameter from networkequipment, disclosed in the first embodiment, is used.

(3-2) The network equipment that configures, for a small cell, whetherto use the ES policy unique to a small cell notifies another cell of theconfiguration as to whether to use the ES policy unique to a small cellof the small cell.

The following four, (1) and (4), will be disclosed as specific examplesof the interface used in notification of an instruction to permit orprohibit switch-off from another cell or a coverage macro cell to asmall cell.

(1) Notification is made in broadcast information. A new indicator isadded. The specific example (1) excels the specific examples (2) and (3)of the interface described below in that an instruction to permit orprohibit switch-off needs not to be notified individually per small cellwhen, for example, a large number of small cells are installed in acell. The following two, (1-1) and (1-2), will be disclosed as specificexamples of the method of receiving the broadcast information of a smallcell: (1-1) when broadcast information is received during neighbor cellsearch, and (1-2) when update notification of the system information ofanother cell or a coverage macro cell is received.

(2) Notification is made by an X2 interface. An indicator may be addedto the existing message. The following three, (2-1) to (2-3), will bedisclosed as specific examples of the existing message.

(2-1) “CELL ACTIVATION REQUEST” message (see Chapter 8.3.1 of Non-PatentDocument 15), which is a message for requesting switch-on of a cellbeing switched off in the conventional ES policy. The ES-relatedinformation can be transmitted and received in the same message,avoiding a communication system becoming more complicated.

(2-2) “LOAD INFORMATION” message (see Chapter 9.1.2.1 of Non-PatentDocument 15). As described below, when the status of radio resources isused in the judgment as to whether to permit or prohibit switch-off, theradio-resource-related information can be transmitted and received inthe same message, avoiding a communication system becoming morecomplicated.

(2-3) “eNB Configuration Update” message (see Chapter 8.3.5 ofNon-Patent Document 15). The cell configuration or status informationcan be transmitted and received in the same message, avoiding acommunication system becoming more complicated.

(3) Notification is made by an S1 interface via an MME. An indicator maybe added to the existing message. A specific example of the existingmessage will be disclosed below. “eNB Configuration Update” message (seeChapter 8.7.4 of Non-Patent Document 16). The cell configuration orstatus information can be transmitted and received in the same message,avoiding a communication system becoming more complicated.

(4) A new interface may be provided.

Disclosed below are specific examples of the judgment as to whether topermit or prohibit switch-off from another cell or a coverage macro cellto a small cell.

Another cell or a coverage macro cell prohibits switch-off if its ownload is high. Thus, the small cell, which has been instructed toprohibit switch-off, does not switch itself off by its own judgment. TheUE located in the coverage of the small cell can accordingly use thesmall cell, eliminating a lack of radio resources in another cell or acoverage macro cell. For the same reason, the processing load of anothercell or a coverage macro cell can be reduced.

Another cell or a coverage macro cell permits switch-off when its ownload is low. This causes the small cell that has received an instructionto permit switch-off to switch itself off by its own judgment. Thus, ifthe small cell switches itself off, another cell or a coverage macrocell can properly communicate with a UE being served by the small cellbeing switched off because the other cell or the coverage macro cell hasa low load. Also, power saving is achieved by the small cell switchingitself off.

Next, a specific example of the sequence of a communication system inthe case where the solution in the second embodiment is used will bedescribed with reference to FIGS. 18 and 19. FIGS. 18 and 19 show anexample sequence of the communication system in the second embodiment.FIG. 18 is continuous with FIG. 19 at a boundary BL2. Steps of FIGS. 18and 19, corresponding to those of FIGS. 16 and 17, will be denoted bythe same step numbers and common description will be omitted.

In Step ST1401, a small cell is installed. The small cell performsneighbor cell search in Step ST1402 and then moves to Step ST1403.

The small cell judges whether it is installed in the coverage of a macrocell in Step ST1403, thereby judging whether a coverage macro cell ispresent. If judging in Step ST1403 that it is not installed in thecoverage of a macro cell, the small cell judges that no coverage macrocell is present and then moves to Step ST1500. If judging in Step ST1403that it is installed in the coverage of a macro cell, the small celljudges that a coverage macro cell is present and then moves to StepST1501.

In Step ST1500, the small cell determines to use the conventional ESpolicy. The small cell may determine not to use the ES policy unique tothe small cell. Upon completion of the process of Step ST1500, the smallcell ends the process in installation and then moves to another process.The processes after Step ST1500 are not characteristic of the presentinvention, which will not be described here.

In Step ST1501, the small cell determines to use the ES policy unique tothe small cell.

In Step ST1502, the coverage macro cell maps an indicator to permit orprohibit switch-off of the small cell in the coverage to broadcastinformation, and then transmits the broadcast information after themapping to the small cell.

In Step ST1503, the small cell receives the broadcast information. Thesmall cell may receive the broadcast information of the coverage macrocell.

In Step ST1504, the small cell judges whether switch-off is permitted.In this example, the small cell judges whether the broadcast informationreceived in Step ST1503 contains the indicator to permit switch-off,thereby judging whether switch-off is permitted.

If judging in Step ST1504 that the broadcast information contains theindicator to permit switch-off, the small cell judges that switch-off ispermitted and then moves to Step ST1505. If judging in Step ST1504 thatthe broadcast information contains no indicator to permit switch-off,the small cell judges that switch-off is not permitted and then returnsto Step ST1503.

In Step ST1505, the small cell judges whether to switch itself off byits own judgment. If judging in Step ST1505 to switch itself off, thesmall cell moves to Step ST1506 of FIG. 19. If judging in Step ST1505not to switch itself off, the small cell returns to Step ST1503. Or, thesmall cell may repeat the process of Step ST1505.

In the example shown in FIGS. 18 and 19, the process of Step ST1505 isperformed after the processes of Steps ST1503 and ST1504. Alternatively,the order of the processes may be changed such that the processes ofSteps ST1503 and ST1504 are performed after the process of Step ST1505.

In Step ST1506, the small cell switches itself off. In Step ST1507, thesmall cell notifies the coverage macro cell that it has switched itselfoff.

In the example shown in FIGS. 18 and 19, the process of Step ST1507 isperformed after the process of Step ST1506. Alternatively, the order ofthe processes may be changed such that the process of Step ST1506 isperformed after the process of Step ST1507. In this case, the process ofnotifying the coverage macro cell that the small cell is to switchitself off may be performed as the process of Step ST1507.

In Step ST1508, the coverage macro cell judges whether the load hasbecome higher. If judging in Step ST1508 that the load has becomehigher, the coverage macro cell moves to Step ST1509. If judging in StepST1508 that the load has not become high, the coverage macro cellrepeats the process of Step ST1508.

In Step ST1509, the coverage macro cell notifies the small cell of aswitch-on request to request the small cell to switch itself on.

In Step ST1510, the small cell judges whether to have received theswitch-on request from the coverage macro cell. If judging to havereceived the switch-on request in Step ST1510, the small cell moves toStep ST1511. If judging to have received no switch-on request in StepST1510, the small cell returns to Step ST1509.

In Step ST1511, the small cell switches itself on. In Step ST1512, thesmall cell notifies the coverage macro cell that it has switched itselfon.

In the example shown in FIGS. 18 and 19, the process of Step ST1512 isperformed after the process of Step ST1511. Alternatively, the order ofthe processes may be changed such that the process of Step ST1511 isperformed after the process of Step ST1512. In this case, the small cellmay perform the process of notifying the coverage macro cell that it isto switch itself on as the process of Step ST1512.

Next, a specific example of another sequence of the communication systemin the case where the solution of the second embodiment is used will bedescribed with reference to FIGS. 20 and 21. FIGS. 20 and 21 showanother example sequence of the communication system in the secondembodiment. FIG. 20 is continuous with FIG. 21 at a boundary BL3. In theexample shown in FIGS. 20 and 21, processes different from those ofFIGS. 18 and 19 are performed. Steps of FIGS. 20 and 21, correspondingto those of FIGS. 16 to 19, will be denoted by the same step numbers andcommon description will be omitted.

In Step ST1401, a small cell is installed. The small cell performsneighbor cell search in Step ST1402 and then moves to Step ST1403.

If judging in Step ST1403 that it is not installed in the coverage of amacro cell, the small cell judges that no coverage macro cell is presentand then moves to Step ST1500. If judging in Step ST1403 that it isinstalled in the coverage of a macro cell, the small cell judges that acoverage macro cell is present and then moves to Step ST1404. In StepST1404, the small cell notifies the coverage macro cell of its owncapability.

In Step ST1406, the coverage macro cell, which has received thecapability of the small cell in Step ST1404, selects a configurationsuitable for the capability of the small cell. Specifically, thecoverage macro cell selects a configuration parameter suitable for thecapability of the small cell. In this example, the coverage macro cellselects the ES policy unique to the small cell as an ES policy andselects a configuration parameter in which the ES policy unique to thesmall cell is configured.

In Step ST1601, then, the coverage macro cell notifies the small cell ofthe configuration parameter selected in Step ST1406. In this example,the coverage macro cell notifies the small cell of the configurationparameter in which the ES policy unique to the small cell is configuredas an ES policy.

In Step ST1602, the small cell determines to use the ES policy unique tothe small cell in accordance with the configuration parameter receivedin Step ST1601.

In Step ST1603, the coverage macro cell notifies the small cell in itscoverage of an indicator to permit or prohibit switch-off.

In Step ST1604, the small cell receives the indicator to permit orprohibit switch-off from the coverage macro cell. Upon receipt of theindicator to permit or prohibit switch-off, the small cell moves to StepST1504.

In Step ST1504, the small cell judges whether switch-off is permitted.In this example, the small cell judges whether the indicator received inStep ST1604 is an indicator to permit switch-off, thereby judgingwhether switch-off is permitted.

If judging in Step ST1504 that the received indicator is an indicator topermit switch-off, the small cell judges that switch-off is permittedand then moves to Step ST1505. If judging in Step ST1504 that thereceived indicator is not an indicator to permit switch-off, that is,that the received indicator is an indicator to prohibit switch-off, thesmall cell judges that switch-off is not permitted and then returns toStep ST1603.

The small cell judges whether to switch itself off by its own judgmentin Step ST1505 and, if, judging to switch itself off, moves to StepST1506 of FIG. 21. If judging in Step ST1505 not to switch itself off,the small cell returns to Step ST1603. Or, the small cell may repeat theprocess of Step ST1505.

Then, in Steps ST1506 to ST1512, the processes similar to those of StepsST1506 to ST1512 of FIG. 19 are performed.

The second embodiment achieves the following effects. An ES operationsuitable for the small cell is achieved. Energy saving, which reflectsthe load, is achieved as a communication system. An ES operation of thesmall cell, corresponding to the installation place of the small cell,is achieved. In the installation of a small cell, the ES policy of thesmall cell can be configured without an operator. This achieves easyoperation and administration by the operator when a small cell isinstalled.

First Modification of Second Embodiment

A first modification of the second embodiment solves a problem similarto that of the second embodiment. Described below is a solution in thefirst modification of the second embodiment.

The first modification of the second embodiment newly provides the ESmethod unique to a small cell, which differs from the conventionalmethod. Specifically, a switch-off method unique to a small cell and amethod of requesting re-activation unique to a small cell are newlyprovided in the conventional ES policy. These methods do not newlyprovide an ES policy per se and thus avoid a communication systembecoming more complicated than the method of newly providing an ESpolicy unique to a small cell of the second embodiment. Also, acommunication system having excellent backward compatibility can beconstructed. This achieves an ES operation optimum for a communicationsystem in which small cells are introduced.

The solution in the first modification of the second embodiment will bespecifically described below. The following four, (1) to (4), will bedisclosed as specific examples of the ES method unique to a small cell.

(1) As a specific example of the switch-off method unique to a smallcell, a small cell makes an inquiry to another cell about whether it canswitch itself off before switch-off. Another cell may be a concentratedcontrol node for the small cell. Or, another cell may be an ESconcentrated control node (also referred to as an “ES concentrator”).Or, if a small cell is installed in the coverage of another cell, thesmall cell may make an inquiry to the other cell about whether it canswitch itself off.

If a response to the inquiry about whether it can switch itself off isswitch-off permission, the small cell switches itself off.

If a response to the inquiry about whether it can switch itself off isswitch-off prohibition, the small cell does not switch itself off. Whennotifying switch-off prohibition, another cell may also notify aprohibition period. The small cell does not switch itself off during theswitch-off prohibition period.

The small cell located outside the coverage of another cell may operateas follows. The small cell can switch itself off by its own judgment. Inswitch-off, the small cell notifies a neighbor cell that it is to switchitself off. When requested to switch itself on from a neighbor cell, thesmall cell switches itself on.

(2) As a specific example of the switch-off method unique to a smallcell, if a small cell is installed in the coverage of a macro cell, thesmall cell makes an inquiry to the coverage macro cell about whether itcan switch itself off before switch-off.

If a response to the inquiry about whether it can switch itself off isswitch-off permission, the small cell switches itself off.

If a response to the inquiry about whether it can switch itself off isswitch-off prohibition, the small cell does not switch itself off. Whennotifying switch-off prohibition, the coverage macro cell may alsonotify a switch-off prohibition period. The small cell does not switchitself off during the switch-off prohibition period.

A small cell located outside the coverage of the macro cell operates asfollows. The small cell can switch itself off by its own judgment. Inswitch-off, the small cell notifies a neighbor cell that it is to switchitself off. When requested to switch itself on from the neighbor cell,the small cell switches itself on.

(3) As a specific example of the method of requesting re-activationunique to a small cell, when notifying a small cell in a switch-offstate of a switch-on request, a neighbor cell configures a switch-offprohibition period. In notifying a switch-on request to a cell that hasnotified that the cell is a small cell when notifying switch-off, theneighbor cell may configure a switch-off prohibition period. Or, theneighbor cell may be a concentrated control node for the small cell. Or,the neighbor cell may be an ES concentrated control node (also referredto as an “ES concentrator”). The small cell does not switch itself offduring the switch-off prohibition period.

(4) As a specific example of the method of requesting re-activationunique to a small cell, when notifying a small cell in a switch-offstate of a switch-on request, a coverage macro cell configures aswitch-off prohibition period. In notifying a switch-on request to acell that has notified that the cell is a small cell when notifyingswitch-off, the coverage macro cell may configure a switch-offprohibition period. The small cell does not switch itself off during theswitch-off prohibition period.

As described above, Non-Patent Document 1 discloses that an OAMconfigures a switch-off determining policy used by an eNB but does notdisclose details thereof. In other words, Non-Patent Document 1 does notdisclose that another cell is inquired about whether switch-off isenabled before switch-off. As described above, Non-Patent Document 1discloses that an OAM configures a re-activation request policy used bya neighbor eNB but does not disclose details thereof. In other words,Non-Patent Document 1 also does not disclose a switch-off prohibitionperiod.

Specific examples of the method of judging whether a small cell isinstalled in the coverage of another cell or a macro cell are similar tothose of the first embodiment, which will not be described here.

Specific examples of the method in which a small cell judges whether atarget cell is a macro cell in cell search are similar to those of thefirst embodiment, which will not be described here.

The following two, (1-1) and (1-2), will be disclosed as specificexamples of the operation in the case where a plurality of other cellsare present in the specific example (1) of the ES method unique to asmall cell.

(1-1) A small cell follows the instructions of all the other cells.Specifically, the small cell makes inquiries to all the other cells. Thesmall cell, which has been instructed to permit switch-off from all theother cells, operates as follows. The small cell can switch itself offby its own judgment. In switch-off, the small cell notifies a neighborcell that it is to switch itself off. When requested to switch itself onfrom a neighbor cell, the small cell switches itself on.

The small cell, which has been instructed to prohibit switch-off from atleast another cell, operates as follows. The small cell cannot switchitself off by its own judgment. Specifically, the small cell does notswitch itself off.

(1-2) A small cell follows the instruction of the representative othercell among a plurality of other cells. Specifically, the small celldetermines the representative other cell.

More specifically, the small cell makes an inquiry to the representativeother cell. The small cell, which has been instructed to permitswitch-off from the representative other cell, operates as follows. Thesmall cell can switch itself off by its own judgment. In switch-off, thesmall cell notifies the representative other cell or a neighbor cellthat it is to switch itself off. When requested to switch itself on fromthe representative other cell or the neighbor cell, the small cellswitches itself on.

The small cell, which has been instructed to prohibit switch-off fromthe representative other cell, operates as follows. The small cellcannot switch itself off by its own judgment. In other words, the smallcell does not switch itself off.

The following two, (1-2-1) and (1-2-2), will be disclosed as specificexamples of the method of determining the representative other cell.

(1-2-1) A coverage cell having the highest reception quality in cellsearch by a small cell is the representative other cell.

(1-2-2) A coverage cell that has performed a configuration suitable forthe capability of a small cell using the first embodiment is therepresentative other cell.

The following two, (2-1) and (2-2), will be disclosed as specificexamples of the operation when a plurality of coverage macro cells arepresent in the specific example (2) of the ES method unique to a smallcell.

(2-1) A small cell follows the instructions of all the coverage macrocells.

Specifically, the small cell makes inquiries to all the coverage macrocells. The small cell, which has been instructed to permit switch-offfrom all the coverage macro cells, operates as follows. The small cellcan switch itself off by its own judgment. In switch-off, the small cellnotifies all the coverage macro cells that it is to switch itself off.When requested to switch itself on from the coverage macro cell, thesmall cell switches itself on.

The small cell, which has been instructed to prohibit switch-off from atleast one coverage macro cell, operates as follows. The small cellcannot switch itself off by its own judgment. In other words, the smallcell does not switch itself off.

(2-2) A small cell follows the instruction of a representative coveragemacro cell among a plurality of coverage macro cells. Specifically, thesmall cell determines a representative coverage macro cell.

More specifically, the small cell makes an inquiry to a representativecoverage cell. The small cell, which has been instructed to permitswitch-off from the representative coverage macro cell, operates asfollows. The small cell can switch itself off by its own judgment. Inswitch-off, the small cell notifies a representative coverage macro cellor a coverage macro cell that it is to switch itself off. When requestedto switch itself on from the representative coverage macro cell or thecoverage macro cell, the small cell switches itself on.

The small cell, which has been instructed to prohibit switch-off fromthe representative coverage macro cell, operates as follows. The smallcell cannot switch itself off by its own judgment. In other words, thesmall cell does not switch itself off.

The following three, (2-2-1) to (2-2-3), will be disclosed as specificexamples of the method of determining a representative coverage macrocell.

(2-2-1) A coverage macro cell having the highest reception quality incell search by a small cell is a representative coverage macro cell.

(2-2-2) A coverage macro cell that has performed a configurationsuitable for the capability of a small cell using the first embodimentis a representative coverage macro cell.

(2-2-3) A macro cell to be operated together with a small cell in themacro support mode is a representative coverage macro cell. Specificexamples of the macro cell to be operated together with a small cell aresimilar to those of the first embodiment, which will not be describedhere.

The following two, (3-1) and (3-2), will be disclosed as specificexamples of the operation when a plurality of other cells are present inthe specific example (3) of the ES method unique to a small cell.

(3-1) A small cell follows the instructions of all the other cells.

Specifically, the small cell follows the longest switch-off prohibitionperiod among the switch-off prohibition periods notified from all theother cells. The small cell cannot switch itself off by its own judgmentduring the switch-off prohibition period. In other words, the small celldoes not switch itself off.

(3-2) A small cell follows the instruction of the representative othercell among a plurality of other cells. Specifically, the small celldetermines the representative other cell.

More specifically, the small cell follows a switch-off prohibitionperiod notified from the representative other cell. The small cellcannot switch itself off by its own judgment during the switch-offprohibition period notified from the representative other cell. In otherwords, the small cell does not switch itself off.

Specific examples of the method of determining the representative othercell are similar to the specific examples of the method of determiningthe representative other cell in (1-2) of the specific example (1) ofthe ES method unique to a small cell, which will not be described here.

The following two, (4-1) and (4-2), will be disclosed as specificexamples of the operation when a plurality of coverage macro cells arepresent in the specific example (4) of the ES method unique to a smallcell.

(4-1) A small cell follows the instructions of all the coverage macrocells.

Specifically, the small cell follows the longest switch-off prohibitionperiod among the switch-off prohibition periods notified from all thecoverage macro cells.

The small cell cannot switch itself off by its own judgment during theswitch-off prohibition period. In other words, the small cell does notswitch itself off.

(4-2) A small cell follows the instruction of a representative coveragemacro cell among a plurality of coverage macro cells. Specifically, thesmall cell determines a representative coverage macro cell.

More specifically, the small cell follows a switch-off prohibitionperiod notified from the representative coverage macro cell. The smallcell cannot switch itself off by its own judgment during the switch-offprohibition period notified from the representative coverage macro cell.

Specific examples of the method of determining a representative coveragemacro cell are similar to the specific examples of the method ofdetermining a representative coverage macro cell in (2-2) of thespecific example (2) of the ES method unique to a small cell, which willnot be described here.

The following three, (1) to (3), will be disclosed as specific examplesof the method in which another cell or a coverage macro cell judgeswhether a cell being switched off is a small cell.

(1) A cell broadcasts an indicator as to whether it is a small cell.Another cell or a coverage macro cell receives broadcast information ofa target cell and checks an indicator as to whether the target cell is asmall cell.

(2) Another cell or a coverage macro cell makes judgment on the basis ofa capability parameter of a small cell, which is notified from the smallcell when the small cell is installed using the first embodiment. If thecapability parameter includes an indication that a target cell is asmall cell, the other cell or the coverage macro cell judges that thetarget cell is a small cell. Or, the other cell or the coverage macrocell may judge a cell, which has notified its own capability parameter,as a small cell. The cell may also notify its own identifier. Or, thecell may also notify an indicator as to whether the cell is a small cellwhen notifying a neighbor cell that the cell is to switch itself off.

(3) Another cell or a coverage macro cell judges a cell, which has madean inquiry about whether it can switch itself off before switch-offusing the specific examples (1) and (2) of the ES method unique to asmall cell, as a small cell. The cell may also notify its ownidentifier.

Specific examples of the entity that configures whether to use the ESmethod unique to a small cell and of the method of judging whether touse the ES method unique to a small cell in the small cell are similarto the specific examples of the entity that configures whether to usethe ES policy unique to a small cell and of the method of judgingwhether to use the ES policy unique to a small cell in the small cell inthe second embodiment, which will not be described here.

The following three, (1) to (3), will be disclosed as specific examplesof the interface used by a small cell to notify another cell or acoverage macro cell whether the small cell can switch itself off beforeswitch-off.

(1) Notification is made by an X2 interface. An indicator may be addedto the existing message. Disclosed below as a specific example of theexisting message is the “eNB Configuration Update” message (see Chapter8.3.5 of Non-Patent Document 15). This is a message used when a cellnotifies a neighbor cell that it is to switch itself off by its ownjudgment in the case of switching-off by the existing ES method. TheES-related information can accordingly be transmitted and received inthe same message, avoiding a communication system becoming morecomplicated.

(2) Notification is made by an S1 interface via an MME. An indicator maybe added to the existing message. Disclosed below as a specific exampleof the existing message is the “eNB Configuration Update” message (seeChapter 8.7.4 of Non-Patent Document 16). The cell configuration orstatus information can be transmitted and received in the same message,avoiding a communication system becoming more complicated.

(3) A new interface may be provided.

The following three, (1) to (3), will be disclosed as specific examplesof the interface used when another cell or a coverage macro cellnotifies a small cell of a switch-off prohibition period.

(1) Notification is made in broadcast information. A new indicator isadded. The specific example (1) excels the specific examples (2) and (3)of the interface described below in that a switch-off prohibition periodneeds not to be individually notified per small cell when, for example,a large number of small cells are installed in a cell. The followingthree, (1-1) to (1-3), will be disclosed as specific examples of themethod of receiving broadcast information in a small cell: (1-1) whenbroadcast information is received in neighbor cell search, (1-2) whenupdate notification of system information of another cell or a coveragemacro cell is received, and (1-3) a small cell, which has received aswitch-on request from another cell or a coverage macro cell, receivesbroadcast information of the other cell or the coverage macro cell andchecks a switch-off prohibition period.

(2) Notification is made by an X2 interface. An indicator may be addedto the existing message. The following three, (2-1) to (2-3), will bedisclosed as specific examples of the existing message.

(2-1) “CELL ACTIVATION REQUEST” message (see Chapter 8.3.1 of Non-PatentDocument 15), which is a message of requesting a cell being switched offto switch itself on in the conventional ES operation. The ES-relatedinformation can be transmitted and received in the same message,avoiding a communication system becoming more complicated.

(2-2) “LOAD INFORMATION” message (see Chapter 9.1.2.1 of Non-PatentDocument 15). When the status of radio resources is used for judgment inthe case of permitting or prohibiting switch-off, as described below,the radio-resource-related information can be transmitted and receivedin the same message, avoiding a communication system becoming morecomplicated.

(2-3) “eNB Configuration Update” message (see Chapter 8.3.5 ofNon-Patent Document 15). The cell configuration or status informationcan be transmitted and received in the same message, avoiding acommunication system becoming more complicated.

(3) Notification is made by an S1 interface via an MME. An indicator maybe added to the existing message. Disclosed below as a specific exampleof the existing message is the “eNB Configuration Update” message (seeChapter 8.7.4 of Non-Patent Document 16). The cell configuration orstatus information can be transmitted and received in the same message,avoiding a communication system becoming more complicated.

(4) A new interface may be provided.

The following two, (1) and (2), will be disclosed as specific examplesof how a switch-off prohibition period is defined.

(1) A period after switch-on of a small cell, that is, a relative time.

(2) A period of switch-off prohibition, such as a period from 9 a.m. to5 p.m., that is, an absolute time.

Described below is a specific example of the judgment as to whetheranother cell or a coverage macro cell configures a switch-offprohibition period for a small cell.

Another cell or a coverage macro cell judges, for higher load thereof,to configure a switch-off prohibition period. As a result, a small cellis not to switch itself off by its own judgment during a switch-offprohibition period. This allows a UE located in the coverage of thesmall cell to use the small cell, eliminating a lack of radio resourcesin the other cell or the coverage macro cell. Besides, for the samereason, the processing load of the other cell or the coverage macro cellcan be reduced.

Another cell or a coverage macro cell judges, for a lower load thereof,not to configure a switch-off prohibition period. As a result, a smallcell switches itself off by its own judgment. Thus, the other cell orthe coverage macro cell has a low load, enabling the other cell or thecoverage macro cell to properly communicate with a UE being served bythe small cell if the small cell switches itself off. Also, the smallcell, which switches itself off, can save energy.

Next, a specific example of the sequence of a communication system whenthe solution in the first modification of the second embodiment is usedwill be described with reference to FIGS. 22 and 23. FIGS. 22 and 23show an example sequence of the communication system in the firstmodification of the second embodiment. FIG. 22 is continuous with FIG.23 at a boundary BL4. Steps of FIGS. 22 and 23, corresponding to thoseof FIGS. 16 to 19, will be denoted by the same step numbers and commondescription will be omitted.

In Step ST1401, a small cell is installed. The small cell performsneighbor cell search in Step ST1402 and then moves to Step ST1403.

In Step ST1403, the small cell judges whether it is installed in thecoverage of a macro cell, thereby judging whether a coverage macro cellis present. If judging in Step ST1403 that it is not installed in thecoverage of a macro cell, the small cell judges that no coverage macrocell is present and then moves to Step ST1700. If judging in Step ST1403that it is installed in the coverage of a macro cell, the small celljudges that a coverage macro cell is present and then moves to StepST1701.

In Step ST1700, the small cell determines to use the conventional ESmethod. The small cell may determine not to use the ES method unique tothe small cell. Upon completion of the process of Step ST1700, the smallcell ends the process in installation and then moves to another process.The process after Step ST1700 is not characteristic of the presentinvention, which will not be described here.

In Step ST1701, the small cell determines to use the ES method unique tothe small cell. When determining to use the ES method unique to a smallcell, the small cell moves to Step ST1505.

In Step ST1505, the small cell judges whether to switch itself off byits own judgment. If judging to switch itself off in Step ST1505, thesmall cell moves to Step ST1506. If judging not to switch itself off inStep ST1505, the small cell repeats the process of Step ST1505.

Then, in Steps ST1506 and ST1507 of FIG. 22 and Steps ST1508 to ST1512of FIG. 23, the processes similar to those of Steps ST1506 to ST1512 ofFIG. 19 are performed.

Then, in Step ST1702 of FIG. 23, the coverage macro cell maps theswitch-off prohibition period of a small cell in the coverage tobroadcast information and then transmits the broadcast information afterthe mapping to the small cell.

The small cell, which has switched itself on in Step ST1511, or thesmall cell, which has received a switch-on request from the coveragemacro cell in Step ST1509, receives the broadcast information from thecoverage macro cell in Step ST1703.

In Step ST1704, the small cell judges whether the broadcast informationreceived in Step ST1703 contains a switch-off prohibition period. Ifjudging in Step ST1704 that the broadcast information contains aswitch-off prohibition period, the small cell moves to Step ST1705. Ifjudging in Step ST1704 that the broadcast information contains noswitch-off prohibition period, the small cell does not perform theprocess of Step ST1705.

In Step ST1705, the small cell does not switch itself off during theswitch-off prohibition period.

Next, a specific example of another sequence of the communication systemwhen the solution in the first modification of the second embodiment isused will be described with reference to FIGS. 24 and 25. FIGS. 24 and25 show another example sequence of the communication system in thefirst modification of the second embodiment. FIG. 24 is continuous withFIG. 25 at a boundary BL5. In the example shown in FIGS. 24 and 25,processes different from those of FIGS. 22 and 23 are performed. Stepsof FIGS. 24 and 25, corresponding to those of FIGS. 16 to 19 and FIGS.22 and 23, will be denoted by the same step numbers and commondescription will be omitted.

In Step ST1401, a small cell is installed. The small cell performsneighbor cell search in Step ST1402 and then moves to Step ST1403.

If judging in Step ST1403 that it is not installed in the coverage of amacro cell, the small cell judges that no coverage macro cell is presentand then moves to Step ST1700. If judging in Step ST1403 that it isinstalled in the coverage of a macro cell, the small cell judges that acoverage macro cell is present and then moves to Step ST1404.

In Step ST1404, the small cell notifies the coverage macro cell of itsown capability. In Step ST1406, the coverage macro cell that hasreceived the capability of the small cell in Step ST1404 selects aconfiguration suitable for the capability of the small cell.Specifically, the coverage macro cell selects a configuration parametersuitable for the capability of the small cell. In this example, thecoverage macro cell selects the ES method unique to the small cell asthe ES method and selects a configuration parameter in which the ESmethod unique to the small cell has been configured.

In Step ST1801, then, the coverage macro cell notifies the small cell ofthe configuration parameter selected in Step ST1406. In this example,the coverage macro cell notifies the small cell of the configurationparameter in which the ES method unique to the small cell has beenconfigured as the ES method.

In Step ST1701, next, the small cell determines to use the ES methodunique to the small cell. When determining to use the ES method uniqueto the small cell, the small cell moves to Step ST1505.

In Step ST1505, the small cell judges whether to switch itself off byits own judgment. If judging to switch itself off in Step ST1505, thesmall cell moves to Step ST1802. If judging not to switch itself off inStep ST1505, the small cell repeats the process of Step ST1505.

In Step ST1802, the small cell makes an inquiry to the coverage macrocell about whether or not it can switch itself off.

In Step ST1803, the coverage macro cell notifies the small cell of aresponse to the inquiry about whether the small cell can switch itselfoff, which has been received in Step ST1802. The content of the responseis switch-off permission or switch-off prohibition.

In Step ST1504, then, the small cell judges whether switch-off ispermitted. In this example, the small cell judges whether or not thecontent of the response received in Step ST1803 is switch-offpermission, thereby judging whether switch-off is permitted.

If judging in Step ST1504 that the content of the response received inStep ST1803 is switch-off permission, the small cell judges thatswitch-off is permitted and then moves to Step ST1506 of FIG. 25. Ifjudging in Step ST1504 that the content of the response received in StepST1803 is not switch-off permission, in other words, if judging that thecontent is switch-off prohibition, the small cell judges that switch-offis not permitted and then returns to Step ST1505.

Then, in Steps ST1506 to ST1512 of FIG. 25, processes similar to thoseof Steps ST1506 to ST1512 of FIG. 19 are performed.

The first modification of the second embodiment can achieve the effectssimilar to those of the second embodiment.

Second Modification of Second Embodiment

Described below is a problem solved in a second modification of thesecond embodiment. 3GPP has discussed a small cell cluster but has notdiscussed the ES operation in the case where a small cell cluster isintroduced. It means that 3GPP has not discussed an ES operation optimumfor the introduction of a small cell cluster.

Described below is a solution in the second modification of the secondembodiment. In addition to the second embodiment, this modificationnewly provides an ES policy suitable for a small cell cluster.

A specific example of the ES policy suitable for a small cell cluster isthe ES operation per small cell cluster.

The entity that controls the ES operation per small cell cluster isreferred to as a “small cell cluster ES concentrator.”

Specific examples of the small cell cluster are the same as those of thefirst embodiment, which will not be described here.

The following three, (1) to (3), will be disclosed as specific examplesof the ES operation per small cell cluster.

(1) A small cell cluster ES concentrator judges whether any one smallcell in a small cell cluster is switched on. If any one small cell inthe small cell cluster is switched on, the small cell cluster ESconcentrator instructs all the small cells included in the cluster toswitch themselves on and also instructs all the small cells included inthe cluster to prohibit switch-off.

(2) A small cell cluster ES concentrator judges whether a UE in theconnected state (CONNECTED) is located while being served by any onesmall cell of a small cell cluster. If a UE in the connected state(CONNECTED) is located while being served by any one small cell of thesmall cell cluster, the small cell cluster ES concentrator instructs allthe small cells included in the cluster to switch themselves on and alsoinstructs all the small cells included in the cluster to prohibitswitch-off.

If no UE in the connected state (CONNECTED) is located while beingserved by all the cells in the small cell cluster, the small cellcluster ES concentrator instructs all the small cells included in thecluster to permit switch-off. Or, the small cell cluster ES concentratormay instruct all the small cells included in the cluster to switchthemselves off.

(3) Combination of (1) and (2) above.

The following six, (1) to (6), will be disclosed as specific examples ofthe small cell cluster ES concentrator.

(1) Scheduling entity in cell aggregation.

(2) Coordinated control entity for CoMP (also referred to as a “CoMPconcentrator”).

(3) Operation administration and maintenance (OAM). The OAM mayconfigure an ES policy. If the small cell cluster ES concentrator is theOAM, the entity that configures an ES policy is the same as the smallcell cluster ES concentrator. This eliminates the need for exchanging,for example, the ES policy information of cells, avoiding acommunication system becoming more complicated.

(4) Coverage macro cell.

(5) MME.

(6) HeNBGW.

The small cell cluster ES concentrator and the entity that manages thesmall cell cluster may be the same. The entity that manages a small cellcluster stores a list of small cells included in the small cell cluster,eliminating the need for exchanging information of a list of small cellsincluded in the small cell cluster. This avoids a communication systembecoming more complicated.

Specific examples of the entity that manages a small cell cluster arethe same as those of the first modification of the first embodiment,which will not be described here.

The following two, (1) and (2), will be disclosed as specific examplesof the method in which a small cell cluster ES concentrator recognizes“whether a UE in the connected state (CONNECTED) is located while beingserved by any one small cell of a small cell cluster.”

(1) The small cell cluster ES concentrator is notified of theinformation about the connection between a UE and each cell being servedby an MME, which is owned by the MME.

(2) Each small cell notifies a small cell cluster ES concentrator ofinformation as to whether a UE in the connected state (CONNECTED) ispresent.

Disclosed below is a specific example of the method in which a smallcell cluster ES concentrator recognizes “whether any one small cell in asmall cell cluster is switched on.” In the ES operation, when switchingitself off, a small cell notifies a small cell cluster ES concentratorthat it switches itself off. In switch-on, the small cell notifies thesmall cell cluster ES concentrator that it has switched itself on. Innotifying switch-on or switch-off, the small cell may also notify anindicator as to whether it is a small cell. The cell may also notify itsown identifier.

The second modification of the second embodiment achieves the followingeffects. An ES operation optimum for the introduction of a small cellcluster is achieved. If a small cell cluster is introduced, an ESoperation is achieved per small cell cluster. Effects thereof will bedescribed below by way of specific examples.

If a small cell cluster is a group of small cells whose schedulingentities are the same, the ES operations of small cells that may be usedin cell aggregation can be made the same. This enables the selection ofsmall cells used in cell aggregation without taking into account the ESoperation of each small cell. Cell aggregation can therefore becontrolled easily.

If a small cell cluster is a group of small cells according to theirinstallation places, the ES operations of small cells, which are desiredto be switched off or on on the same condition, can be made the same.The same condition means, for example, that small cells installed in aschool are desired to be switched off when the school is closed.

If a small cell cluster is a group of small cells belonging to the sameCoMP cooperating set, ES operations of small cells, which may be used inCoMP, can be made the same. This enables the selection of small cellsused in CoMP without taking into account the ES operation of each smallcell. CoMP can therefore be controlled easily.

Third Modification of Second Embodiment

Described below is a problem solved in a third modification of thesecond embodiment. Probably, a large number of small cells areinstalled. A small cell probably has a relatively narrow coverage area.Thus, considered here is a case where the policy of determiningswitch-off used by an eNB relates to, for example, a UE in the connectedstate (CONNECTED). When a UE in the connected state (CONNECTED) moves ata constant speed, small cells are probably switched more frequently thanmacro cells because of a difference in coverage area. Generally, a cellneeds a preparation period from switch-off to switch-on in which thecell is available to a UE as usual, that is, the UE and the cell cantransmit and receive data. Frequent switching leads to a lack of thepreparation period, so that a moving UE cannot transmit and receive datacontinuously. Also, frequent switching actually needs controlinformation and the like, so that ES effects may not be achieved.

The following two, (A) and (B), will be disclosed as the solutions inthe third modification of the second embodiment.

(A) One small cell can belong to a plurality of small cell clusters, andan ES operation can be achieved per small cell cluster with the use ofthe second modification of the second embodiment. A specific examplewill be described with reference to FIG. 26. FIG. 26 is a diagram forexplaining the concept in the solution of the third modification of thesecond embodiment. Small cells individually configure coverages 1901 to1917 in a predetermined range. For easy understanding, FIG. 26 does notshow each small cell and shows each small cell by its coverage. Thefollowing description will describe the respective small cells byreferences “1901” to “1917” indicating their coverages.

A cluster a includes small cells 1910, 1911, 1914, 1915, and 1916. Acluster b includes the small cells 1911 and 1916 and small cells 1907,1908, 1912, 1913, and 1917. A cluster c includes the small cells 1907,1910, and 1911 and small cells 1901, 1902, 1905, and 1906.

In a location 1919, a UE 1900 is in the connected state with the smallcell 1911. The UE 1900 transmits and receives user data to and from thesmall cell 1911.

If a UE in the connected state (CONNECTED) is located in the small cell1911, the small cells included in the cluster a, the cluster b, and thecluster c are switched on because the small cell 1911 is included in thecluster a, the cluster b, and the cluster c. The small cells included inthe cluster a, the cluster b, and the cluster c are prohibited fromswitching themselves off.

Described below is the case where the UE 1900 moves from the location1919 to a location 1918.

In the location 1918, the UE 1900 is in the connected state with thesmall cell 1907. The UE 1900 transmits and receives user data to andfrom the small cell 1907.

If the UE in the connected state (CONNECTED) is located in the smallcell 1907, the small cells included in the cluster b and the cluster care switched on because the small cell 1907 is included in the cluster band the cluster c. The small cells included in the cluster b and thecluster c are prohibited from switching themselves off.

The above reveals that the small cell 1907 that handles the transmissionand reception by the UE 1900 after the UE moves is switched on while theUE 1900 is located in the location 1919 and the small cell 1911 ishandling the transmission and reception by the UE 1900. As describedabove, the small cell is switched on before the UE moves, securing apreparation period, which enables continuous transmission and receptionby a moving UE.

Considered here is a case where the UE 1900 moves from the location 1919to the location 1918, and then slightly moves back to the location 1919.It is revealed that the small cell 1911 is switched on while the UE 1900is located in the location 1918 and the small cell 1907 is handling thetransmission and reception by the UE 1900. If the UE slightly movesback, the small cell where the UE was present before moving is notswitched off immediately. Thus, a preparation period is secured,enabling continuous transmission and reception by a moving UE. The smallcell where the UE was present before moving is not immediately switchedoff merely as a result of the UE moving, preventing frequent switching.

In the specific example (A), small cells included in a small cellcluster can be determined statically or semi-statically. Compared withthe specific example (B), thus, the entity that notifies switch-offprohibition or switch-off permission can easily judge a notificationdestination, leading to a reduced processing load.

(B) An ES policy suitable for a small cell cluster is newly provided.The following two, (1) and (2), will be disclosed as specific examplesof the ES policy suitable for a small cell cluster.

(1) A neighbor small cell for the small cell in which a UE in theconnected state (CONNECTED) is located is switched on. A neighbor smallcell for the small cell in which a UE in the connected state (CONNECTED)is located is prohibited from switching itself off.

Or, a neighbor small cell for the small cell in which a UE thattransmits and receives a user data plane (U plane) is located isswitched on. A neighbor small cell for the small cell in which a UE thattransmits and receives a user data plane (U plane) is prohibited fromswitching itself off.

(2) A neighbor small cell for the small cell in which a UE in theconnected state (CONNECTED) is not located is permitted to switch itselfoff.

Alternatively, a neighbor small cell for the small cell in which a UEthat transmits and receives a user data plane (U plane) is not locatedis permitted to switch off.

In the location 1919 shown in FIG. 26, the UE 1900 is in the connectedstate with the small cell 1911. Or, the UE 1900 transmits and receivesuser data to and from the small cell 1911.

Neighbor small cells for the small cell 1911 in which a UE in theconnected state (CONNECTED) is located, for example, the small cells1906, 1907, 1910, 1912, 1915, and 1916 are switched on. Neighbor smallcells for the small cell 1911 in which the UE in the connected state(CONNECTED) is located, for example, the small cells 1906, 1907, 1910,1912, 1915, and 1916 are prohibited from switching themselves off.

Described below is the case where the UE 1900 moves from the location1919 to the location 1918.

In the location 1918, the UE 1900 is in the connected state with thesmall cell 1907. Or, the UE 1900 transmits and receives user data to andfrom the small cell 1907.

Neighbor small cells for the small cell 1907 in which the UE in theconnected state (CONNECTED) is located, for example, the small cells1902, 1903, 1906, 1908, 1911, and 1912 are switched on. Neighbor smallcells for the small cell 1911 in which the UE in the connected state(CONNECTED) is located, for example, the small cells 1902, 1903, 1906,1908, 1911, and 1912 are prohibited from switching themselves off.

As described above, it is revealed that the small cell 1907 that handlesthe transmission and reception by the UE 1900 after the UE 1900 moves isswitched on while the UE 1900 is located in the location 1919 and thesmall cell 1911 is handling the transmission and reception by the UE1900. The small cell is switched on before the UE moves as describedabove, securing a preparation period, which enables continuoustransmission and reception by a moving UE.

Considered here is a case where the UE 1900 moves from the location 1919to the location 1918 and then slightly moves back to the location 1919.It is revealed that the small cell 1911 is switched on while the UE 1900is located in the location 1918 and the small cell 1907 is handling thetransmission and reception by the UE 1900. If the UE slightly movesback, the small cell where the UE was present before moving is notswitched off immediately. This secures a preparation period, enablingcontinuous transmission and reception by a moving UE. Also, a small cellwhere the UE was present before moving is not switched off immediatelymerely as a result of the UE moving, preventing frequent switching.

The following four, (1) to (4), will be disclosed as specific examplesof the entity that notifies each small cell of switch-on, switch-offprohibition, or switch-off permission.

(1) MME, which can make judgment easily because it holds informationabout the connection between a UE and each cell being served by an MME.

(2) Small cell in which a UE in the connected state (CONNECTED) islocated, which can make judgment easily because it holds its connectioninformation.

(3) Coverage macro cell.

(4) ES concentrated control node (ES concentrator).

The following three, (1) to (3), will be disclosed as specific examplesof the interface used in notification of switch-on, switch-offprohibition or switch-off permission.

(1) Notification is made by an X2 interface. An indicator may be addedto the existing message. The following three, (2-1) to (2-3), will bedisclosed as specific examples of the existing message.

(1-1) “CELL ACTIVATION REQUEST” message (see Chapter 8.3.1 of Non-PatentDocument 15), which is a message requiring a cell being switched off toswitch itself on in the conventional ES policy. The ES-relatedinformation can be transmitted and received in the same message,avoiding a communication system becoming more complicated.

(1-2) “LOAD INFORMATION” message (see Chapter 9.1.2.1 of Non-PatentDocument 15). Whether a UE in the connected state (CONNECTED) is presentalso means whether a radio resource is allocated to the UE, enabling thetransmission and reception of the radio-resource-related information inthe same message. This avoids a communication system becoming morecomplicated.

(1-3) “eNB Configuration Update” message (see Chapter 8.3.5 ofNon-Patent Document 15). The cell configuration or status informationcan be transmitted and received in the same message, avoiding acommunication system becoming more complicated.

(2) Notification is made by an S1 interface. An indicator may be addedto the existing message. A specific example of the existing message willbe disclosed below. “MME Configuration Update” message (see Chapter8.7.5 of Non-Patent Document 16). No new message is provided, avoiding acommunication system becoming more complicated.

(3) A new interface may be provided.

The third modification of the second embodiment achieves the followingeffects. When a UE moves between small cells, the small cell being amoving destination is switched on before the UE moves. This secures apreparation period, enabling continuous transmission and reception by amoving UE. Also, the small cell where the UE was present before movingis not immediately switched off merely as a result of the UE moving,preventing frequent switching because of a slight moving of the UE.

Third Embodiment

Described below is a problem solved in a third embodiment. The smallcell probably has a relatively narrow coverage area. Considered here isa case where the policy of determining switch-off used by an eNB relatesto, for example, a UE in the connected state (CONNECTED). The frequencyat which a UE in the connected state (CONNECTED) is located while beingserved by a small cell is probably lower than by a macro cell. In otherwords, switching of small cells probably occurs more frequently thanswitching of macro cells.

The problem solved in the third embodiment will be described withreference to FIG. 15. For example, here, the UE1 is located in thecoverage 1304 of the small cell 1305. The UE1 camps on the small cell1305 (is in an idle state). In other words, the UE is not in theconnected state. The small cell 1305 switches itself off by its ownjudgment because there is no UE in the connected state (CONNECTED).

The UE1 in the idle state performs cell reselection. The UE1 selects themacro cell 1303 having the coverage 1303 overlying the small cell 1305.

The UE1 reselects the macro cell 1303 and checks the TAC of the macrocell 1303.

If the TAC of the macro cell 1303 differs from the TAC of the small cell1305, the UE1 processes TAU of the macro cell 1303.

There occurs a problem in which if no contrivance is made, TAU from theUE frequently occurs by small cells, which are probably installed inlarge numbers.

Described below is a solution in the third embodiment. The coveragemacro cell and the small cell are to have the same TAC. Further, thesmall cells having the same coverage macro cell are to have the sameTAC.

The following two, (1) and (2), will be disclosed as specific examplesof the method of causing a coverage macro cell and a small cell to havethe same TAC.

(1) As in the first embodiment, the already installed network equipmentconfigures a TAC concomitantly with the configuration suitable for thecapability of the small cell. The network equipment configures the sameTAC as the TAC of the coverage macro cell.

(2) A small cell configures a TAC. The small cell performs cell search(neighbor cell search) when installed and, if a coverage macro cell ispresent, checks the TAC of the coverage macro cell and configures itsown TAC to the checked TAC.

The following two, (1) and (2), will be disclosed as specific examplesof the operation of the small cell that has configured a TAC.

(1) A small cell maps a TAC to broadcast information to notify UEs beingserved thereby of the TAC.

(2) A small cell reports the configured TAC to an MME.

When a coverage macro cell notifies a UE being served by a small cell ofthe system information of the small cell, the TAC of the small cell maybe the same as the TAC of the coverage macro cell to be omitted. Thisreduces traffic.

The third embodiment achieves the following effects. In other words, ifswitching of small cells occurs more frequently than switching of macrocells or if a large number of small cells are installed, transmissionsof a TAU from a UE can be reduced.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

DESCRIPTION OF REFERENCE NUMERALS

1301 and 1303, coverage of macro eNB (macro cell); 1302 and 1304,coverage of small eNB (small cell); 1305, 1306, and 1901 to 1917, smallcell (coverage); and 1900, UE.

The invention claimed is:
 1. A communication system comprising: acommunication terminal device including at least a controller and awireless interface circuit to perform radio communication; at least onebase station device including a least a processor and a wirelessinterface circuit to configure a plurality of cells capable of radiocommunication with the communication terminal device; and an entityincluding a processor coupled to at least one communication interfaceand configured to control the plurality of cells, wherein each of theplurality of cells is configured to switch between a normal operationand an energy saving operation, the plurality of cells being groupedinto a predetermined cell cluster according to an energy saving (ES)policy of each of the plurality of cells, and the entity is configuredto control switching between the normal operation and the energy savingoperation of the plurality of cells.
 2. The communication systemaccording to claim 1, wherein the entity is configured to controlswitching between the normal operation and the energy saving operationper cell cluster.
 3. The communication system according to claim 1,wherein the plurality of cells include a cell belonging a plurality ofcell clusters.
 4. A communication system comprising: a communicationterminal device including at least a controller and a wireless interfacecircuit to perform radio communication; at least one base station deviceincluding a least a processor and a wireless interface circuit toconfigure a plurality of cells capable of radio communication with thecommunication terminal device; and an entity including a processorcoupled to at least one communication interface and configured tocontrol the plurality of cells, wherein each of the plurality of cellsis configured to switch between a normal operation and an energy savingoperation, the plurality of cells being grouped into a predeterminedcell cluster according to an energy saving (ES) policy of each of theplurality of cells, the entity is configured to control a cell being amoving destination of the communication terminal device to shift to thenormal operation before the communication terminal device moves into thecell, and the entity is configured to control switching between thenormal operation and the energy saving operation per cell cluster.